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BOOK 570. M52 v. 1 c. 1 



i ii inn mil iiii ii linn mi mi ii 

3 T153 00137361 E 



with Special Reference to Man 


Director of the Department of Zoology, Marquette University 
Late Professor of Biology, University of Dallas 






Copyright 1922-1924-1928 

Printed in the United States 
of America 


To My Students 

whose loyalty and appreciation have been my 

inspiration throughout the years this 

book has been in preparation. 

Digitized by the Internet Archive 
in 2013 


With the ninety-third adoption of this volume as a classroom text, 
the need for another new edition arises. A number of changes have 
been made, not only in the interest of later scientific findings, but also 
where the text or illustration lent itself to some misinterpretation. Sev- 
eral illustrations have been redrawn so as to make them more usable 
by the student. 

Again, the author and the publisher welcome any suggestions or 
criticisms which will make further editions of this book of still greater 

July 1, 1928. 


Although the first edition of this work came from the press too 
late for use in the first semester, the extraordinary reception accorded 
it, especially by medical educators and medical journals, necessitated 
immediate preparations for a second edition. 

The work has been gone over carefully, and various changes have 
been made where it has been found that the student would profit by 
such changes and the entire work has been reset. It is now issued in 
two volumes so as to accommodate those schools which, presenting only 
general biology, require but the first half of the subject matter. 

Two objections have been raised by several critics: (1) that the 
chapters "Why to Study," "How to Study," and "The Coordination of 
Subjects Studied," have as much place in any textbook on Chemistry or 
Physics as they have in a work on Biology, and that in reality they have 
no place in either ; and (2) that the apparent lack of organization in the 
third portion of the work (now the latter half of Volume II) prevented 
the student from obtaining a clear-cut line of demarcation between 
Anatomy and Physiology. 

Regarding the first objection: There are actually only two real 
coordinating subjects in the college curriculum — Philosophy and 
Biology. And, as very few students of the sciences ever take any of 
the philosophical courses, the only department left, where coordination 
can be driven home effectively, is Biology. 

Further, the author spent practically an entire school year visiting 
the leading universities in this country and abroad to find how and where 
to improve the various courses. He found deans and professors alike 
agreeing that the most important thing that could be given a student 
during the first years of his college work was the manner and the 
means of learning how to study, why to study, and how to coordinate 
the subjects studied. 

He then took the laboratory courses as given in our American 
schools of medicine so as to obtain first-hand information as to what 
professional students actually need. This work is the result. 

Regarding the second objection : There are no such artificial lines 
of demarcation in the living organism as are used in the laboratory. 
Anatomy and Physiology are most intimately interwoven in life. There- 
fore, in order that the student obtain a realization of the artificial labora- 
tory grouping, as well as the actual conditions in the living organism, 
the first half of the book keeps Anatomy and Physiology separate and 
distinct, except where the two can be shown to be intimately related, 
while the third portion of the work interweaves the two branches. This 
apparent lack of organization and separation of the two branches of 
science was, therefore, of deliberate intent. 

January 1, 1924. 


Teachers of the Biological Sciences have often observed that : 

(1) The majority of American college students are the children 
of parents who have not had a college training and, therefore, have no 
proper conception of what a college course means, nor an understanding 
of the reasons that lead educators to place certain studies in the curricu- 
lum instead of others. 

(2) The work done by the average student up to his entry into 
college has neither taught him how to study, nor how to coordinate the 
work of the various courses he has had. 

(3) The technical words he has met with have not been analyzed, 
so that he has no conception of their derivation, and, consequently, of 
their true meaning. He has largely memorized whatever was learned 
with little understanding of meanings. 

(4) The professional world (especially of medicine and dentistry) 
is in general accord with the idea that "General Biology" or "General 
Zoology" should be followed by "Introductory Embryology" and "Com- 
parative Anatomy." 

(5) Most texts on the biological sciences either try to make the 
subject matter entirely too easy, and thus forget to mention the many 
points of prime interest to professional students, or they try to cover 
the entire range of animal biology, thus burdening both book and student 
with matter that will be forgotten as soon as examinations are passed. 

(6) The student is, therefore, confronted with several alternatives : 
Either he takes the "easy" course and feels that because he was told so 
little, there is but little to be told. Or if the more detailed course has 
been taken, he finds that it has helped him but little, if any, in his chosen 
field, and he is rightfully disappointed. 

(7) The terminology in Botany, Zoology, and Medicine is by no 
means identical, and much must be relearned by professional students. 

(8) A textbook usually confines itself to "Type Forms" or to 
"General Principles." In either case, the student suffers for want of the 
half that is left untold. 

(9) Results of scientific work are often given, such as the life- 
cycle of the Malarial Parasite, without showing in detail the type of 
work necessary to bring about those results, thus preventing the student 
from gaining one of the most valuable lessons of his scientific course. 

(10) Medical and Dental educators, as well as students themselves, 
are constantly complaining of the insufficient stress placed on Histology 
and Neurology in the preliminary courses, as it is in these fields that so 
many students later find their greatest difficulties. 

(11) Medical educators insist that in a few years all medical 
schools must add a course in Medical Zoology. The students who are 

now being prepared for these courses must obtain an adequate number 
of examples of animal parasites in their premedical studies, or they will 
not be able to profit fully when such later course is taken. 

(12) The student now purchases three, and often four, texts for 
his biological work, none of which is a true continuation of its 

(13) When studying a given biological problem, constant reference 
must be made to facts and findings of various kinds, for the purpose of 
checking up and coordinating the work one is doing. If a student must 
seek through many volumes for such references, he is all too likely not 
to look for any at all ; whereas, if he has but to turn a few pages, he 
will almost invariably search out many. 

Being confronted with points such as these, and wishing to obtain 
the professional student's point of view as well as an understanding of 
his difficulties, the author has taken the regular laboratory courses 
offered in American schools of medicine, and has built this book on what 
experience has taught him to hold most valuable. 

Therefore, he begins (1) by showing the student why to study, 
and (2) how to study and how to coordinate the various courses of the 
curriculum. (3) The glossary is made quite complete by giving both 
derivations and pronunciations of all technical words used in the text, 
and the student is then asked to write them out in the parentheses left 
blank for that purpose. (4) "General Biology" is followed by "Intro- 
ductory Embryology" of the Chick and Frog, with a general statement 
regarding Mammalian Forms, thus presenting to the student the begin- 
nings of a Comparative Study. This, then, is followed by "Comparative 
Anatomy" where constant comparisons are not only made, but where 
back references are brought into play to force a repetition, so essential 
to a full understanding of all scientific work. 

(5) One subject (the Frog) is treated exhaustively, so that the 
student will not be burdened with too good an opinion of his own 
knowledge of even so humble a thing as the frog, while principles are 
always presented after the facts have been shown upon which those 
principles rest. 

(6) The entire work is concentrated and by no means "easy." The 
goal of the student is kept in mind. 

(7) The terminology which the professional student will use later 
is always borne in mind and stressed. 

(8) "Type Forms" are studied, but only in so far as these are 
necessary to a full and complete understanding of both the anatomy 
and physiology of the animal, and to furnish the facts on which to build 
interpretations and principles. 

(9) In such work as that on the Malarial Parasite, the result of 
scientific work is first shown so as to cause the student to wonder how 
such a mass of intricate detail could ever have been discovered. Then 
a detailed account of the painstaking and intelligent effort necessary to 
make such findings valuable is given. 

(1.0) Histology and Genetics are stressed, because in all biological 

work a thorough knowledge of the cell and tissues is a prerequisite for 
further work, .and Neurology, because of its tremendous importance in 
all biological, psychological, and medical fields. 

(11) Examples, wherever possible, have been chosen in so far as 
they add to, or detract from, human welfare, for, after all, students of 
Education, Law, Philosophy, Psychology, Sociology, Theology, Eco- 
nomics, Engineering, Medicine, and Dentistry are, and must be, most 
interested in Man. 

(12) All that is needed for two complete years of biological work 
is contained within this work. Each part logically follows the part 
preceding, and thus not only saves the student considerable time and 
expense, but also serves him as a sort of continual reference work in his 
future professional years of study. Both the Bee and the Grasshopper 
have been included so that teachers may use their preferred form. 

(13) Then, too, the student who has his entire course of study 
before him in a single work, often, of his own volition, reads much more 
than he normally would were the subject matter scattered through sev- 
eral texts, for it is an easy matter to refer to another closely related 
subject if the reference can be found by merely turning a few pages. 

The book is so written that it can be used as a text for General 
Biology, General Zoology (by merely omitting Chapters XV and XVI), 
for Introductory Embryology, and for Comparative Anatomy. 

Where only one year is given to biological work, as in many Dental 
Schools, it is suggested that the first semester be given to "General 
Biology" or "General Zoology" made up of selected chapters from the 
first half of the text, while the second semester be confined to the higher 
forms such as Dogfish, Turtle, and Cat or Rabbit, as found in "Com- 
parative Anatomy." 

The "Laboratory Manual for Biology and Embryology," by Pro- 
fessor John Giesen, should be used with "General Biology" and "Intro- 
ductory Embryology." 

Dr. L. H. Hyman's "A Laboratory Manual for Comparative Verte- 
brate Anatomy" (University of Chicago Press) is being used for the 
comparative work in Anatomy. 

Long bibliographies have not been given in this book, as these are 
seldom consulted by a student during the first two years of his college 
career. However, as all of the books mentioned on pages 12 and 13 
should be in every college library, those who wish such bibliographies 
can find the best in Kellicott's "Chordate Development," Patten's "The 
Early Embryology of the Chick," and Kingsley's "Comparative Anatomy 
of Vertebrates." 

It is much more important for the student to know HOW to Com- 
pile a Bibliography than to look over one already made. Therefore, in 
the author's classes a different subject is assigned each student to look 
up, for the purpose of compiling a bibliography of everything written on 
that subject for the past forty years. Such subject may be taken from 
any index of the Journal of the American Medical Association. 

Forty years are chosen because it is about that many years ago that 

some of the larger indices were compiled, and it is essential that the 
student be forced to go through all the indices year by year. If the 
indices are not found in the smaller towns and cities, the bibliography 
can be made during one of the vacations when the student passes 
through some of the larger cities where there is a medical or scientific 

The more important indices published in the English Language are: 

The Zoological Record (published yearly by the Zoological Society of London. 
Each volume gives a complete list of the works and publications relating to 
zoology in all its branches that have appeared during the preceding year. The 
first volume was for the year 1864). 

The Index Medicus (Found in any Medical Library). 

Index Catalogue of the Surgeon General's Office. 

International Catalogue of Scientific Literature, "Zoology," "Botany," "General 
Biology." (Pub. by Harrison & Sons, 45 St. Martin's Lane, London.) 

For popular articles : 

The Reader's Guide to Periodical Literature. 

The International Index to Periodicals. (Before Jan., 1921, The Reader's Guide 
to Periodical Literature Supplement.) 

The books which have been of greatest service to the author are : 
On General Biology 

Parker and Haswell, "Text-book of Zoology." 

L. A. Borradaile, "A Manual of Elementary Zoology." 

Shipley and MacBride, "Zoology." 

R. W. Hegner, "College Zoology." 

J. G. Needham, "General Biology." 

Linville and Kelly, "A Text-book in General Zoology." 

O. H. Latter, "The Natural History of Some Common Animals." 

Schull, Larue, and Ruthven, "Principles of Animal Biology." 

A. M. Marshall, "The Frog." 

S. J. Holmes, "The Biology of the Frog." 

H. S. Pratt, "A Manual of the Common Invertebrate Animals." 

Ward and Whipple, "Fresh-Water Biology." 

Sanderson and Jackson, "Elementary Entomology." 

Leland O. Howard, "The Insect Book." 

J. H. and Anna B. Comstock, "A Manual of the Study of Insects." 

Frank E. Lutz, "Fieldbook of Insects." 

J. W. Folsom, "Entomology with special reference to its Biological and 

Economic Aspects." 
Riley and Johannsen, "Handbook of Medical Entomology." 
W. T. Caiman, "The Life of Crustacea." 
R. W. Hegner, "The Germ-Cell Cycle in Animals." 

W. E. Agar, "Cytology, with Special Reference to the Metazoan Nucleus." 
L. Doncaster, "An Introduction to the Study of Cytology." 
L. W. Sharp, "Introduction to Cytology." 

C. Hill, "A Manual of Normal Histology and Organography." 
Krause-Schmahl, "A Course in Normal Histology." 
W. E. Castle, "Genetics and Eugenics." 

E. G. Conklin, "Heredity and Environment in the Development of Man." 
C. B. Davenport, "Heredity in Relation to Eugenics." 
East and Jones, "Inbreeding and Outbreeding." 
H. E. Walter, "Genetics." 

T. H. Morgan, "A Critique of the Theory of Evolution." 
S. J. Holmes, "The Evolution of Animal Intelligence." 
M. F. Washburn, "The Animal Mind." 
H. S. Jennings, "Behavior of the Lower Organisms." 

Eric Wasmann, "Instinct and Intelligence in the Animal Kingdom." 
James Johnstone, "The Philosophy of Biology." fj 

A. D. Darbishire, "An Introduction to a Biology and Other Papers. 
Vernon L. Kellogg, "Darwinism Today." 

Wm. A. Locy, "Biology and Its Makers." 

H. F. Osborn, "From the Greeks to Darwin." 

C. E. and E. A. Bessey, "Essentials of College Botany." 

Bergen and Davis, "Principles of Botany." 

C. S. Gager, "Fundamentals of Botany." 
Wm. C. Stevens, "Plant Anatomy." 
Strasburgher's "Textbook of Botany." 

D. H. Campbell, "A University Textbook of Botany." 
Coulter, Barnes, and Cowles, "Textbook of Botany." 

I. F. and W. D. Henderson, "A Dictionary of Scientific Terms." 

On Embryology 

F. R. Lillie, "The Development of the Chick." 
W. E. Kellicott, "Chordate Development." 

B. M. Patten, "The Early Embryology of the Chick." 
Prentiss and Arey, "Textbook of Embryology." 

On Comparative Anatomy 

G. C. Bourne, "An Introduction to the Study of Comparative Anatomy." 
J. S. Kingsley, "Comparative Anatomy of Vertebrates." 

L. Vialleton, "Elements de Morphologie des Vertebres."^ 

Schimkewitch, "Lehrbuch d. vergl. Anatomie d. Wirbelthiere." 

H. H. Newman, "Vertebrate Zoology." 

H. W. Wilder, "History of the Human Body." 

Parker and Haswell, "A Textbook of Zoology." 

L. H. Hyman, "A Laboratory Manual for Comparative Vertebrate Anatomy." 

H. S. Pratt, "A Course in Vertebrate Zoology." 

Reighard and Jennings, "Anatomy of the Cat." 

Davison and Stromsten, "Mammalian Anatomy, with special .reference to the 

O. C. Bradley, "A Guide to the Dissection of the Dog." 
Hans Gadow, "Amphibia and Reptiles." 

B. F. Kaupp, "The Anatomy of the Domestic Fowl." 

C. J. Herrick, "An Introduction to Neurology." 
Emil Villiger, "Brain and Spinal Cord." 

S. W. Ransom, "The Anatomy of the Nervous System." 

The author wishes at this point to thank all those who have assisted 
him in any way. Thanks are due to Professors Wm. A. Locy, F. R. 
Lillie, H. S. Pratt, C. W. Ballard, Dr. L. H. Hyman, and Mr. W. C. 
Clute, and their publishers, as well as to Professor J. H. McGregor, 
for permission to use various cuts from their published works. Credit 
is given in the legend of each cut. Thanks are due Professors J. A. Bick 
of Loyola University, Edward Menager of the University of Santa Clara, 
Wm. Atwood of the Milwaukee Normal School, and Dr. Peter P. Finney 
of the University of Dallas for reading much of the manuscript and 
offering valuable suggestions. 

Thanks are due for detailed reading and technical criticism of the 
manuscript to the following: Professor Richard A. Muttkowski, of the 
University of Idaho, for going over the greater portion of the entire 
manuscript; Dr. L. H. Hyman, of the University of Chicago, for going 
over the portion devoted to "Comparative Anatomy" ; Professor Eben 
J. Carey, of Marquette University, for going over the entire portion 

devoted to "Embryology" ; Professors W. N. Steil of the University of 
Wisconsin, J. G. Brown of the University of Arizona and the Carnegie 
Desert Botanical Laboratory, and Sister Mary Ellen, of Santa Clara Col- 
lege, for going over the portions on Botany; Professors Joseph Jastrow, 
of the University of Wisconsin, and George A. Deglman, of Marquette 
University, for reading the portions devoted to Psychology ; Professor 
John B. Kremer, of Marquette University, for reading the portions 
devoted to Geology and Paleontology; Professor Edward Miloslavich, 
late of the University of Vienna, for reading those portions on Immunity 
and Pathology ; Professor Alfred V. Boursy, for reading the glossary, 
and Professor Robert Bauer, for reading the chapter on Coordination. 

Thanks are due Mr. Leo Massopust, Mr. Lane Newberry, and Mr. 
Frank Leibly for the many and painstaking drawings they have made, 
and to Mr. Arthur Vollert, Mr. Frank Krause, Mr. Gervase Flaherty, 
Mr. Norman O'Neill, Mr. Frank Freiburger, Mr. Robert Schodron, Miss 
Phyllis Schnader, Miss Irma Gall, and Miss Nathalie Hart for the many 
hours of assistance rendered in seeing the book through the laborious 
processes of printing. 

The author's appreciation must be extended to his fellow charter 
members of the Baconian Society, Professors Walter Abel, Alfred V. 
Boursy, John Giesen, and Edward Miloslavich, for assistance and criti- 
cism rendered in discussing innumerable points at their meetings. 

And lastly, the author would be remiss in his duty did he not 
express his special thanks and appreciation to his co-worker of many 
years, Professor John Giesen, whose loyalty and willingness to assist 
in every way have made many additional hours of work possible on 
this book. 


Marquette University, 

Milwaukee, Wisconsin, 

June 25, 1922, 




WHY STUDY 19-26 


HOW TO STUDY — Taking of Notes — Clipping Interesting Items — Points 

to be Considered 27-33 

Physics — English — Foreign Languages — Philosophy — Psychology — 

Logic— Ethics 34-42 

THE FROG — External Features — Internal Structure — The Digestive Sys- 
tem — Glands — The Circulatory System — Principal Divisions of the Cir- 
culatory System — The Heart — The Arteries — The Veins — Respiration — 
The Excretory System — The Nervous System — The Central Nervous 
System — The Spinal Cord — The Peripheral Nervous System — The Sym- 
pathetic System — The Sense Organs — The Eye — The Ear — The Olfactory 
Organ — The Tongue — Touch and Pressure — The Skeleton — The Axial 
Skeleton — The Vertebral Column — The Appendicular Skeleton — The 

Muscular System — Reproductive Organs — The Fat Bodies 43-87 


THE CELL— Cell Inclusion and Cell Products 88-93 

Organic Chemistry — Protoplasm — Cell Division (Mitosis) — The Real 
Meaning of Mitosis — Maturation and Elementary Embryology — Fertili- 
zation — Blastulation and Gastrulation 94-108 


HISTOLOGY OF THE FROG— The Four Fundamental Tissues 109-117 



THE PROTOZOA — Amoeba— Movement— Behavior— Euglena— External 
and Internal Features — Locomotion — Nutrition — Encystment — Repro- 
duction — Behavior — Volvox — Plasmodium Malariae — Paramoecium — 
Behavior — Pathogenic Protozoa — Flagellates of Uncertain Position — 

Summary of Important Facts 122-157 

Meaning of Chromosomes in Inheritance — Weismann's Contribution to 

Biology — Mendel's Contribution to Biology 158-165 

GENETICS — The Mechanism of Heredity — Applications of Weismann's 

and Mendel's Laws 166-172 

ANIMAL PSYCHOLOGY— Differences Between Objective and Subjec- 
tive—Between Behaviorists and Introspectionists — Between Materialists 
and Spiritualists — Between Dualists and Monists — Mind — Soul — Struc- 
tural Psychology — Functional Psychology — Nerve Arc — Reflex Action — 
Memory -^-Tropisms — Instinct — Habits — Learning — Thinking — Reason- 
ing—Trial and Error Method 173-185 

INTERMEDIATE ORGANISMS— Haematococcus—Pleurococcus— Photo- 
synthesis — Yeasts — Bacteria 186-194 


IMMUNITY — Natural — Artificial — Active — Passive — Antitoxins — Recep- 
tors — Complements — Antigens — Antibodies — Opsonins — Agglutination — 

Anaphylaxis — Methods Used 195-202 

THE PLANT-WORLD— Simple Plants— Thallophytes— Vaucheria— The 
Fungi — Pathogenic Fungi — Diseases Caused by Fungi of More or Less 
Uncertain Position 203-215 



THE PLANT-WORLD CONTINUED— The Three Higher Groupings— 
Bryophytes — Outline of Life History of Sphagnum — Pteridophytes — 

Spermatophytes — Plant Histology — Pollination — Flowers 216-247 


THE COELENTERATA— Hydra Fusca— Obeiia— Polymorphism— Classi- 
fication 248-258 




THE EARTHWORM— External Appearance— Internal Structure— The 
Digestive System — The Circulatory System — Respiration — The Excre- 
tory System — The Nervous System — Sense Organs — The Reproduc — 
tive System — Oogenesis — Embryology — Behavior — Regeneration — 

Grafting 263-285 


(NEMATHELMINTHES)— The Flatworms— Turbellaria— Trematoda 
— Cestoda — The Threadworms — Nematoda — Intermediate and Uncer- 
tain Forms 286-312 


THE ARTHROPODA — The Crayfish — External Appearance — Serial 
Homologies and Adaptations — The Digestive System — The Circulatory 
System — The Respiratory System — The Excretory System — The Ner- 
vous System — The Special Sense Organs — Muscular System — Reproduc- 
tion — Regeneration — Autotomy — Parasitic Crustacea — Plankton — Ter- 
restrial Crustaceans 313-328 




THE GRASSHOPPER— Importance of Insect Pests— External Appear- 
ance — Internal Anatomy — The Digestive System — The Circulatory Sys- 
tem — The Respiratory System — The Excretory System — The Nervous 
System — The Senses of Insects — Touch — Taste — Smell — Hearing — The 
Muscular System — The Reproductive System — Paedogenesis — Polyem- 

bryony — Alternation of Generations — Embryology — Behavior 333-353 


THE HONEY BEE AND THE FLY— External Appearance of Honey 
Bee — Internal Anatomy and Physiology — The Digestive System — The 
Circulatory System — The Respiratory System — The Excretory Sys- 
tem — The Nervous System — Organs of Special Sense — The Muscular 
System — The Reproductive System — Embryology — Metamorphosis — 
Behavior — Enemies of The Honey Bee — Gynandromorphs — Cross Ferti- 
lization of Plants by Bees — Classification — The Fly — Life History — Fly 

Killers — Parasitic Insects 354-375 


HISTORY OF BIOLOGY— The Most Notable Men and Writings in 

Biology — Chronological Table of Important Biological Events 376-393 


PALEONTOLOGY — Geological Formations — Meaning of Ages or Periods 
— Chart Showing Geological Depths and Ages — Types of Fossils — Early 

Human Bones 394-402 


EVOLUTION — The Different Theories of Evolution — Evidences for 
Evolution — Opposing Arguments — Summary — Criteria for a Satisfac- 
tory Evolutionary Theory 403-415 


CLASSIFICATION— The Earliest Classifiers— Present Method— Tabular 
View of the Classification of Animals as Far as Orders — Groups of 
Invertebrates of More or Less Uncertain Systematic Position — Brief 
Characterizations of the Major Groups of Animals and of Invertebrate 
Groups of Uncertain Position 416-435 



General Biology 



TWO hundred and sixteen (216) separate and distinct combinations 
can be formed by three dice of different design, as shown in the 
drawing (Fig. 1). On the principle of chance, if these three dice 
are thrown an infinite number of times, each one of the 216 combina- 
tions will appear just as often as every other one. 

This is true only if the dice are not weighted. Combinations 
formed by three dice have been chosen because there are usually at least 
three alternatives in any case where a man's judgment or opinion is 
required or asked for. Further, an analogy can be found in the complete 
human individual where the 


Mental, and . 

must ever be considered ; while on the strictly scientific basis, everything 
that a man is, or can be, depends upon the three factors: 


Environment, and 

Or, again, no opinion worth anything can be formed without the fol- 
lowing three factors being taken into consideration : 

Obtaining the facts, 

Reasoning thereon, 

Forming a judgment or conclusion. 
Each dice possessing six sides may be compared to the many facts, 
conditions, or possibilities that go to make up any one of the three great 
factors appearing in the tables above. 

It is self-evident from this that in any given case, where there are 
three factors with six possibilities contingent upon each, unless life's 
dice are weighted by knowledge, a man's opinion stands only one chance 
in 216 of being correct. 

The almost ideal laboratory evidence that substantiates these state- 
ments is found in the fact that out of three thousand cases at one of 
our leading hospitals, the diagnosticians were correct only 53.5 per cent 
of the time. 1 If, at our most important institutions, the ablest and best 
trained men, working with the finest equipment obtainable, are correct 
only approximately one-half the time, it means that on the principle of 
chance, when anyone passes an opinion or comes to a conclusion with- 
out all obtainable knowledge, he cannot approach correctness even this 

^'Diagnostic Pitfalls Identified During a Study of Three .Thousand Autopsies," hy Richard C. 
Cabot, M.D. Journal of the American Medical Association, pp. 2295-2298, Dec. 28, 1912. 


General Biology 

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Fig. 1. 

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three dice of different design). 

Why Study 


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Fig. 1. 

22 General Biology 

The evidence forces the conclusion that, under present conditions, 
if we should know all that it is possible for a human being to know, we 
could be right only about one-half the time. As knowledge is the only 
way in which we can be right even as frequently as this, it follows that 
when an opinion is called forth without any knowledge, a man forms 
approximately 215 erroneous conclusions to every one that is correct. 
The scriptural command becomes intelligible: "Get ye therefore 

It has been said that the evidence from diagnostic sources is almost 
ideal to illustrate the point here made. Everything we do that requires 
an opinion is pure diagnosis. In other words, every time one passes 
a judgment upon the facts presented, it is a diagnosis of some kind, and 
any error in our diagnosis means that no intelligent suggestion can 
come forth as to a remedy, except on the basis of one correct one to 215 
erroneous ones. The diagnosis must be correct or the remedy is absurd 
with the only possible exception of a guess accidentally correct. 

No intelligent person wishes to have his government run, his estate 
adjusted, his house built, or his farm managed upon pure guess work 
in which the chances are that two 1 hundred and fifteen times more wrong 
things will be done than right ones. And this is not only the case in 
medicine, dentistry, and the professions at large, but in the every-day 
business world as well. Dun and Bradstreet, who keep a record of every 
individual entering, as well as every one failing in business, tell us that 
95 out of every 100 men who enter a commercial line for themselves 
fail at some time in their lives. This is due, not only to an ignorance 
of the particular line of work they may enter, but also to ignorance of 
business principles and methods at large. 

To many persons it seems that the purely practically-trained indi- 
vidual is better equipped than he whose training has been theoretical, 
and individuals usually mentioned as examples to illustrate this point 
are among the ablest practically-trained men to be found, who are then 
compared with some of the poorest theoretically- trained. Because a boy 
is sent to college does not mean anything except, that, if he has a capacity 
for the work he takes up, he will be able to get the practical side of 
his study, while in addition he will learn why he does what he does, 
when he does it. Any man with great ability along a given line will 
naturally know more, and be able to work better along that line than 
any man without such capacity who has merely taken some theoretical 
course. But, if we take two men of equal intelligence and capacity, 
who take up, let us say, the plumber's trade, he who has mastered both 
the practical and the theoretical side of his work will always be superior 
to him who has become interested in only one or the other. It must be 
remembered that 

(1) Capacity, 

(2) Opportunity, and 

(3) Application 

are essential to make a master of anyone in anything. 

Why Study 23 

It takes considerable time to show the fruits of any study, and men 
are impatient for results. 

Someone has truly said that the value of education consists in 
knowing a man when you meet one; which means, of course, that any- 
one knowing his subject-matter in a given field will be able to know 
whether one claiming to be an expert in that field speaks truthfully or 
not. It means that we must know about a matter ourselves or we can- 
not intelligently choose worthy leaders. It means, we must be able to 
distinguish gold from dross, real ability from advertising, scientific men 
from those who are simply well known. It means that we must be able 
to distinguish between the real expert and him who* calls himself one, 
remembering that experts do not disagree very much, but those who 
call themselves experts do. 

Whether we like it or not, we must acknowledge that every man 
who has lived and exercised any kind of leadership, good or bad, has 
left his impress upon our generation. All those who have gone on 
before us, together with those living now, as well as those who are to 
come after us, really form a great intellectual democracy, from which 
all but the present generation are removed only in person. The past 
is with us in an overwhelming mass. The unborn are those for whom 
we now labor. All our customs, our traditions, our ideas of conventional 
correctness and wrongness, and our laws were given us by men long 
since passed away. In other words, we are actually ruled by dead men. 

The men who have long since passed away have given us their 
ideas and their thoughts ; but, to us those ideas and thoughts, those laws 
and traditions must be interpreted, and our interpreters of these things 
are our courts. Mr. Taft has said, "I care not who makes the laws, if 
I can but interpret them." It is always meanings, interpretations, which 
are of most value. Now, we know that our judges (our legal inter- 
preters), are practically all college men, which means that, in the final 
analysis, everyone of us is controlled by what our institutions of higher 
learning teach. 

It, therefore, behooves each of us to obtain the requisite knowledge 
before forming an opinion as to whom we shall follow as leaders in 
every walk of life, whether this be in politics or in war, in civil or 
religious life, in law or in medicine, in farming or commercial pursuits, 
or we shall be wrong in nearly everything we do. 

Not possessed of knowledge, a man confuses sincerity with truth, 
forgetting that the most insane of men are intensely sincere, and that 
anyone following sincere but insane theories of life must quite naturally 
reap destruction ; forgetting that to obtain the truth in anything, all the 
facts must be known and a valid interpretation placed upon the facts, 
and this can only be done by considering man in his entirety — in his 
physical, mental, and ethical aspects. 

One must, therefore, weight life's dice with knowledge if correct- 
ness is to be formed in any walk of life, 

24 General Biology 

Nearly every parent desirous of his child's welfare, wishes he could 
leave the child the benefit of his own experience, so that the child might 
profit by his parent's mistakes and not make the same blunders. The 
value of this desire may be appreciated when it is remembered that if 
experience cannot be handed down, there is absolutely no progress. For, 
each individual, instead of starting where his parents left off and con- 
tinuing onward, would necessarily have to begin where they began, and, 
consequently, when life came to a close, the children would be prac- 
tically where their parents had been at the close of their careers. 

Men of the past have, therefore, written their experience in books, 
and we of to-day can profit not only by the experience of our immediate 
parents but by that of our forefathers. 

The laboratory has gone even a little further than this. 

As no one man can work out every detail in the study of a single 
plant or animal without having to take the work of all those into con- 
sideration who have gone before and who have contributed something 
to the knowledge of the particular plant or animal under discussion, so, 
men have gathered into a single grouping the important physical experi- 
ences which have been found convincing to their minds and have called 
such grouping a textbook. 

The study of the subject-matter of a textbook, plus the actual work- 
ing out of these same convincing experiences (now called experiments) 
in the laboratory, cause the student to see the way in which proof is 
obtained for the conclusions men hold. 

In fact, laboratory work, plus a study of the text, is the fulfillment 
of the parent's wish that his child inherit the parent's experience. 

From the experiments which give us conclusive evidence of the 
way some physical process works, we draw our principles. 

Principles are mental tools without which no mental progress is 

In fact, a principle is a law of nature, proved by physical experi- 
ment, to which no exception has been found. Physics presents an excel- 
lent illustration of the value of principles. 1 

Everyone knows that, if a substance, such as iron, which is heavier 
than water, is placed in water, it will sink. Yet iron ships do not sink. 
Why? Because when we speak of anything as "heavier than water" 
we mean that the same quantity of a given substance is heavier than the 
same quantity of water. 

After Archimedes discovered his principle, we knew immediately 
that, if we could bend iron so that it would occupy more cubic feet of 
space than that same number of cubic feet of water would weigh, it 
would be "lighter than water" and would float. 

Heavy iron ships could not, however, be of practical use until some 
one again discovered the principles of steam or electricity, and so they 

x An old Greek named Archimedes, while taking a bath, discovered that when he immersed his 
body in a tub filled with water, his body lost considerable weight. Later he was able to prove 
experimentally that the weight of the water that ran over the top of the tub was exactly the same 
as the weight his body lost while immersed. It was this discovery which made iron ships possible. 

Why Study 25 

were not used until such principle was found. This shows well the 
inter-relationship of things that men do, no matter how many years 
apart the doing may be. 

In Biology, which means the Science of Life (Gr. Bios=life+ 
logos=discourse), we are interested in rinding principles, so that no 
matter in what position we may be placed in later life, we can always 
think back, find our principle, and apply it in a thousand and one differ- 
ent ways. 

The finding of principles, which is real science, must never be con- 
fused with the application of these principles. 

The former is what is meant by science, while the latter is merely 
ordinary labor. 

Inventors apply scientific principles; they are, therefore, not 

Another point to be remembered is that animals (as well as children 
before they reach the so-called age of reason) learn by doing a thing 
over and over, until success or failure comes. If success comes, they 
make such successful endeavor a part of their later life. This is called 
the trial-and-error method of learning. 

Educated men and women do not try out each and everything, but 
come to their conclusions by weighing the evidence for and against a 
principle, and if the principle is found to be worthy of consideration, 
adjust their actions accordingly. 

This is well illustrated if one finds a man attempting the invention 
of a perpetual motion machine. It is a well established principle of 
physics that no more work can be obtained from a machine than is put 
into it, and even then a little loss must be allowed for on account of 
friction. All educated men know this law of nature, and consequently 
do not waste their time on such a fruitless undertaking. But, should 
any one refuse to accept this principle, there is nothing left but to con- 
tinue trying and trying, and coming to the conclusion of its uselessness 
by personal failure. 

The obtaining of principles is then the great work of science. Science 
itself has had many definitions. Some of the best are : 

"Systematized knowledge." 

"Classified common sense." 

"Checking up ;ind getting rid of one's prepossessions." 

"Knowledge gained and verified by exact observation and correct 
thinking, especially when methodically formulated and arranged in a 
rational system." 

In other words, science means a gathering of facts, plus the logical 
meanings or interpretations of these facts. 

The object or purpose of getting the principles which science thus 
finds, is to control nature and to prophesy what will occur when given 
acts are performed.. 

As Biology is the science of life, everything that has anything what- 

26 General Biology 

ever to do with life is really a branch of this science. For example, 
Biology is not a branch of medicine or dentistry, but medicine and 
dentistry are branches of biology where men enter into particular details 
of some division of it. 

Biology, therefore, to the medical student, the dental student, the 
law student, the student of sociology or the student of education, pre- 
sents a sort of bird's-eye view of the fundamental processes upon which 
his whole detailed study must be built, so that he can the better and 
more understanding^ read the valuable and meaningful literature of 
the day and discuss intelligently the very basis on which his every con- 
clusion must rest its truth. In other words, Biology makes it possible 
for the student the better to be able to prevent men who call themselves 
experts, but who are not, from deceptively making people believe they 



SOMEONE has said that to be a cultured man or woman one must 
know something about everything; everything about something; 
and never wilfully or maliciously cause suffering to others, 

No better ideal of what a student of Biology should try to attain has 
ever been written. If all biological principles now known are grasped 
by the student, he can most certainly be said to come as near knowing 
something about everything as it is possible for him to come. 

If he will learn the Frog thoroughly, he can come under the second 
division of importance; and if he will bear the final of the three injunc- 
tions in mind, Biology will be a humanizing and cultural as well as a 
scientific and laboratory study. 

Never read a book, article, or paper, without fountain pen and note- 
book, or note-paper, beside you. 1 

I. Notes are of no value unless they are usable. There are differ- 
ent types of records for different purposes, but those found most con- 
venient by the author are as follows : 

For regular lectures and for general reading — A package of bond 
paper cut to 4x6 inches in size. 

Many such sheets can be carried constantly in the pocket if a little 
heavier paper, or even a piece of cardboard 4x 13 inches in size, is bent 
in the mid-line so as to form a covering for the loose cards. A rubber 
band is placed about the packet. 

A pasteboard file for holding this size of card can be obtained at any 
stationery store, and the cards held together by fasteners can be placed 
under subject headings, ready for access at all times. 

No book or article of value should be read without making a note 
of its name, subject, author, and edition. (This latter is very important, 
because in a year or two another edition may have all its pages differ- 
ently numbered, and even additions and deletions made, so that should 
you quote such a volume and the one to whom you are quoting, looks 
up the quotation in another edition, you will be considered not only in- 
accurate but absolutely untruthful.) 

For clippings — If you own a periodical in which an excellent article 
appears, cut it out. Be sure, however, to write upon it immediately 
the name of the paper from which you clipped it, as well as the year, 
month, and day it appeared. 

1 Probably 95 per cent of all you will ever read, you will want to forget, but the remaining five per 
cent you will need, and need badly when the occasion arises. 

28 General Biology 

Until you have a large accumulation, take ordinary long envelopes 
4^2 x \0y 2 inches. Fold each clipping and place it in such envelope, 
writing its title on the upper left-hand corner under the subject like 
this — 


"Different kinds of Frogs. 

If you do not own the periodical, make out a subject-card just as 
you would for a lecture, and file it under the proper subject. 

For your regular laboratory work you will always have your draw- 
ing book. All notes that pertain to the laboratory will be made in that. 

II. Students will find that it is easier not to take notes on lectures. 1 
Many think they will remember more without notes. This is true if 
the notes are not looked at again ; but, if they are gone over from time 
to time, much that is important will be brought back to mind that 
would otherwise be lost. 

III. Suppose you see an animal, let us say a frog. You must 
observe : 

(1) Its external characteristics. 

(2) Its similarities to the human being. 

(3) Its dissimilarities to the human being. 

(4) Its normal home. 

(5) Its method of life. 

(6) Its relations to its surroundings. 

(7) The conditions under which you came to see it. 

(8) Its actions, normal and when disturbed. 

(9) Its food and whether it is food in turn for other animals. 

(10) How it comes to be where it is? 

(11) Whether or not it remains in the same surroundings through- 
out the year? 

This is all studied on the living frog. Every action of a living thing 
comes under "physiology," which is the science of functions. Physiology 
must, therefore, be studied on the living plant or animal. 

IV. In the laboratory you take up the internal structure, as well as 
the development of the organism, which means in the case of the frog, 
how the animal's eggs grow into a tadpole, and this in turn into a frog. 

V. You are trying to get a complete mental picture of what is 
known about life and you are trying to get a gauge by which to know 
when a thing is true and when it is not; consequently, you must think of 

*0f course, each day, after the lecture, the student is to attempt to repeat all that was said in 
the lecture he has heard, and when he comes to a forgotten point he must consult his notes. 

How To Study 29 

these things you study just as you would if you were trying to use your 
camera for the taking of the picture instead of your mind. 

(1.) Clear away all that is unimportant. 

(2.) Choose a subject. In this case Biology. 

(3.) Have proper perspective (that is, have the relationship 
of everything about your subject in proper form, and do not unduly 
stress any one point). In other words, have you taken everything into 
consideration? For example, you must see to it that some other branch 
of science does not have some points and conclusions which may destroy 
yours, for if a single exception can be found in science, it has disproved 
the law. 

(4.) You must have sufficient light to make the subject stand 
forth and be seen clearly. This implies a proper background — a back- 
ground built up in the study of science by ascertaining what has gone 
before, and what causes have produced the particular historical soil upon 
which the seed of men's ideas have been able to grow. In other words, 
you must have all the facts that can be found if you would have this 
light throw your subject into the full glare of day. You must exclude 
shadows as much as possible. 

(5.) You must see that your subject is in focus, which means 
that in any given case, it must stand forth in sharp relief. It must not 
fade away in the distance and become blurred by your prejudices or 
desires. No vagaries of thought must be permitted. Your reasoning 
must be clear and definite. Your system of knowledge must be built 
up philosophically and logically. 

(6.) You must decide upon how large an opening you will 
allow your lens ; that is, within what narrow limits you are to discuss 
the subject under consideration. 

(7.) You must decide upon the length of time for your ex- 
posure, which, in a scientific treatise, means that you must know that 
sufficient time has elapsed to make your experiments valid and positive. 

(8.) If you read of the results of others, you must take into 
consideration the temperamental makeup of the individual writing as 
well as of yourself and other readers who later pass judgment thereon. 

Remember that just as a football player or musician must keep in 
constant practice, or lose his proficiency, so your brain must have 
DAILY EXERCISE or it will likewise lose its proficiency. 

Remember also, that the man who can, but does not read, has not 
as high an intellectual ranking as he who cannot read; and he who has 
the capacity to think, but does not, ranks lower than he who is born 
without such capacity. 

VI. See that your note-book contains complete drawings and de- 
scriptions of each of the following subjects for every form studied : 

30 General Biology 


1. External Makeup. 

2. Internal Makeup. 

(a) Digestive System. 

(b) Circulatory " 

(c) Respiratory " 

(d) Excretory " 

(e) Nervous 

(f) Skeletal 

(g) Muscular 

(h) Reproductive " 


1. Processes Pertaining to Food. 

(a) Ingestion (taking in food). 

(b) Egestion (throwing out undigested food). 

(c) Digestion (fermentation of ingested substance brought 
about by various secretions). 

(d) Absorption (passing of digested food by osmosis through 
body membranes and making use of inspired oxygen). 

(e) Circulation (carrying absorbed substance to all parts of 
the body). 

(f) Assimilation (the conversion of absorbed non-living mat- 
ter into protoplasm). 

(g) Growth (the increase in size due to additional protoplasm 
being made). 

(h) Reproduction (the production of new organisms similar 
to the parent). 

2. Processes Pertaining to Oxygen. 

(a) Inspiration (taking in oxygen which aerates blood as it 
passes through lungs). 

(b) Oxidation (burning of ingested food). 

(1) Secretion (pouring out substances to be used again). 

(2) Expiration (throwing out C0 2 ). 

(3) Excretion (throwing out used substances in the form 
of urea, uric acid, etc.). 


(4) Energy (a) Applied J Behavior. 

J Locomotion. 
(b) Unapplied^ Light. 

I Electricity. 

How To Study 31 


Any of the processes mentioned in this outline may be made more 
rapid or may be slowed even to the point of complete stoppage by 
mechanical, chemical, and sometimes by mental stimuli. 


(a) Phylum. 

(b) Class. 

(c) Order. 

(d) Family. 

(e) Genus. 

(f) Species. 

V. Finally, remember that your study may be interpreted from any or 
all of the following points of view : 

Both plants and animals must always be thought of when discussing 
living matter, and both are studied in practically the same manner. But 
as no one man can study all about plants or animals, or even about 
everything that pertains to only one plant or animal, scientific men have 
divided their work into group-studies as follows : 

I. Morphology: (Gr. morphe=form) Study of Form. 

1. Promorphology (Gr. pro=first+rnorphe:=:forrn) which 
treats of General Form. 

2. Anatomy: (Gr. anatemno=to cut up) the study of organ- 
isms by dissection. Usually studied on the dead individual; that is, a 
study of Structure. 


(a) Gross, or Macroscopic (Gr. macro=large) that which can 
be seen with the naked eye. 

(b) Microscopic (Gr. micro— small) embracing the study of 
the more minute structures with a microscope. 

Splanchnology (Gr. splanchnos=organs). 
Histology (Gr. histos=:web, or tissue). 
Cytology (Gr. cytos=cell). 
Neurology (Gr. neuron=nerve). 

3. History of Development, that is, a study of the different 
stages through which an organism passes from the moment the fertilized 
cell begins dividing. 

Individual Evolution, Embryology (Gr. en=in+bruo= 

Ontogeny (Gr. on=existing+genna=to begin), the study 

of the individual before birth. 
Racial Evolution (Phylogeny), (Gr. phylon=tribe) the 

study of the race. 

32 General Biology 

4. Teratology (Gr. teras=wonder) the study of malformations 
and monstrosities in organisms. 

II. Physiology. The Study of Functions. 

1. Physiology Proper (Gr. physis=nature) the functional rela- 
tion of part to part and to the whole. 

2. Ecology (Gr. oikos=house) relation of the individual to 
its whole surroundings, or the study of its environment. 

3. Pathology (Gr. pathos=suffering) the study of disease. 
This study also belongs under microscopic anatomy in that disease makes 
many changes in the actual structure of the cells and tissues. 

III. Distribution. 

In Space (Geographical Distribution, often called Zoogeography 

in so far as it affects animals). 

In Time (Paleontology [Gr. palaios=ancient-|-onta=beings] ; 
also called Paleozoology, in so far as it affects the study of fossil remains 
of animals). 

IV. Economic Zoology or Botany, the study of everything living in 
so far as it touches human welfare. 

V. Classification, or Taxonomy (Gr. taxis=arrangement+nomos= 
law), the grouping of plants and animals according to likeness or rela- 

VI. Psychology (Gr. psyche=mind or soul), the study of the 

VII. Sociology (L. socius=companion), the study of animal 
societies and their relation of each member of the society to the other. 
This relationship is sometimes said to be due to the so-called Herd 

VIII. Genetics (Gr. genesis=birth), the science "which seeks to 
account for the resemblances and differences which are exhibited among 
organisms related by descent." 

f Heredity, 
Individual : 1 Environment, 

| Education, \ Instruction, 

^ Einiibung or training. 

Racial: Archeology (Gr. archaios=:ancient), the study of 
ancient findings to ascertain the cultural state of man at different epochs. 

IX. Biometrics (Gr. bios=life+metron=measure), the statistical 
study of life's events or happenings so as to be able to gauge how often 
these same events are likely to take place in the future. 

How To Study 33 

Summarizing the points that must be kept in mind we may say : 

1. You must be able to distinguish between conspicuousness and 

2. You must be able to distinguish between fact and interpretation. 

3. You must be able to distinguish between principles and their 

4. You must be able to discuss all sides of a subject so as to over- 
come scientific bigotry and narrowness. 

5. You must have a knowledge of type-forms as well as the gen- 
eralized biological principles which can be drawn from such knowledge. 

6. You must be able tO' apply all the principles you have learned 
to the human body. 

7. You must know (not only memorize) the meaning of the 
scientific words which you are called upon to use. This will be accom- 
plished by writing in the derivations of the words in the parenthesis 
left open for that purpose. All these can be found in the glossary at 
the end of the volume. 



COMPARATIVELY few students either grasp or understand the 
value of the various studies laid out for them by college authori- 
ties, and it is this lack of grasp and understanding which causes 
them to slur over much of the subject-matter which it is necessary to 
know later. 

As a starting point for this understanding it is essential that one 
grasp fully the underlying object of scientific study. 

In our smaller cities there used to be exhibited a marvelous clock 
which had some ten or fifteen dials upon it, each dial recording some 
important time-element. One, for example, showed the hour of the day, 
another the time of the rising and setting of the sun, another did the 
same for the moon, while still another o;ave the time of the ebb and flow 
of the tides. There was a dial showing the day of the month, so nicely 
arranged that even the 29th day of February in leap year would be 
noted. This clock was so adjusted that there was not only the intonation 
of a chime every quarter-hour, but several interesting events were 
recorded at this same time ; for instance, a cuckoo announcing the quar- 
ter-hour was followed by a rooster strutting forth and crowing, while 
on the hour, a tiny door at one side of the clock opened, and the twelve 
apostles solemnly marched across and disappeared on the opposite side, 
while strangest of all, these apostles did not drag their feet, but actually 
lifted them as they took their hourly walk. 

And all of this elaborate adjustment was the result of a single clock- 
work running by a single winding. 

A living organism is something like that clock, except that it is a 
thousand-fold more complicated, for man can do many times the number 
of things that the clock did. Now, the science of Biology is directed 
just toward the one end of attempting to find what original mechanism 
makes all these complicated actions possible. In other words, in the 
study of Biology we are attempting to find not only life's clock-work 
and the unit structures with which such a mechanism is built, but we 
also try to approach that particular place or time in the history of the 
universe when the first winding took place. 

Chemistry presents an excellent starting-point for further explana- 
tion. In chemistry a compound is analyzed by finding the type of 
molecules that are contained within it, a molecule being the smallest 
obtainable particle of a chemical compound. The molecule, in turn, is 
then reduced to atoms of the various chemical elements, an atom being 
the smallest obtainable particle of a chemical element. The mind can 
readily conceive, however, that there are smaller particles than atoms. 

Co-ordination of Subjects 3d 

As soon as we realize that the black soot which comes from a 
smoking-chimney and the purest of white diamonds are both composed 
of exactly the same chemical atoms — that is, are both pure carbon — we 
find we are not satisfied until some explanation of this remarkable differ- 
ence can be given. 

At this point we must pass to the study of physics, for it is physics 
that deals with the laws of movement and of energy. In reality, it is 
from the physicist, rather than from the chemist, that we obtain an 
explanation as to why the different chemical formulae are what they are. 
The physicist has found that atoms can be broken up into very tiny 
particles, each fragment having the power of attracting or repelling 
other fragments. Such tiny particles are called electrons. 

Knowing this we can evolve a great underlying principle that can 
be applied in -as many different ways as was the principle of Archimedes, 
referred .tt) in a former chapter. 

In fact, the theory of electrons tells us not only why two elements 
chemically alike have a totally different appearance, but it also gives 
us an explanation as to why there are different chemical elements to 
begin with. 

It has been found that if pure carbon is subjected to tremendous 
heat in electric furnaces, followed by the application of thousands of 
pounds of pressure, this carbon will become a diamond. 

The scientific man, learning that this is true, immediately attempts 
to bring about a wider application of his knowledge for the purpose of 
evolving still other principles. Such an one comes to the conclusion, 
then, that it is quite likely that all matter is composed of electrons, and 
that the different forms that matter assumes are due only to varying 
degrees of heat and pressure. 

This means that everything physical — everything that occupies 
space — be it wood, iron, coal, radium, hydrogen, oxygen, or what not — 
is quite probably composed of the same ultimate material or substance, 
but in each case such ultimate substance has been exposed to a different 
quantity of heat and pressure. 

Now, the object of science is to control nature and to prophesy what 
will occur when certain acts are performed. 

It is well to note at this point that science can never explain the 
fundamental why of anything. It cannot tell why metal becomes soft 
when heated, while an egg becomes hard. What science can do, and 
aims to do, is to find how things can be changed from what they are by 
performing a combination of certain definite acts. 

Just as the explanation of how chemical elements come to be what 
they are was found by physicists and not by chemists, thus showing the 
inter-relationship of the two sciences, so man, being a complete entity 
made up of both the physical and the mental, must be considered in his 
double capacity if we are to study him scientifically. 

Physics and chemistry form man's most important studies on the 


General Biology 

physical side. Everyone knows that food is composed of chemical sub- 
stances which, after being taken into the body, pass through many 
chemical changes while being converted into new blood to keep life 
going. The student, however, probably does not know that Louis 
Pasteur, the Father of Bacteriology, was a chemist, and that the whole 
modern conception of medicine is based on the bacteriological findings 
he obtained while working on fermentation experiments in the chemical 
laboratory. The knowledge he there gained was later applied by Lister, 
who made aseptic surgery possible. 

The discovery of oxygen, by -a chemist, directly underlies practically 
every experiment in physiology which can be performed, while the 
great modern surgical advances are largely due to our ability to 
anesthetize the patient. The anesthetics used are nitrous oxide, chloro- 
form, and ether — all products of the chemical laboratory. 

Fig. 2. Diagrams to illustrate tbe different types of levers in their relations to 
the mechanical action of muscles. 

A. Comparison between head, foot and elbow. 

B. Comparison between different actions of foot. 

Most muscles act on bones as levers. In physics there are three types of levers recognized. In 
the first type (I) the fulcrum (F) lies between the place where power (P) is exerted on the lever 
and the point of resistance or load (L). Levers of this kind are frequently met with in the body. 
In A, (I) the weight of the skull tends to bend the head forward, while the force exerted by the 
dorsal muscles of the neck serves to keep the head in position. 

In levers of the second class (II) the point on which power is exerted moves through a greater 
distance than the point of resistance. Speed is thus sacrificed to power. Such levers are rare in 
the body. An example is the body raised on the toes. 

In levers of the third class (III) the point on which force is exerted, moves a less distance 
than the point of resistance, power thus being 1 sacrificed to speed. This is the most common form 
of leverage in the body. The example A (III) is that of the elbow. Here the biceps and brachialis 
muscles are attached only a short distance from the elbow-joint or fulcrum, while the hand is the 
region on which force is exerted. A movement at the point P through a short distance will cause 
L to move a great distance. 

Co-ordination of Subjects 37 

The ability to analyze any product or portion of the body must lie 
with analytical chemistry, while the study of how to build up new 
products comes under synthetic chemistry. All digestion takes place by 
enzymes, and the enzymes of the stomach, for example, will not function 
unless they are placed in an acid- medium, such as the gastric juice. 
Changes in food, or abnormalities of various kinds, may cause an excess 
of this acid, or may prevent a sufficient quantity of the proper quality 
being formed — all such changes are chemical. 

The sttidy of physics in its application to one's body is not so self- 
evident and is often the bug-bear of students. Unfortunately most text- 
books on physics lay stress upon mechanical laws only in their indus- 
trial applications, and fail to show how these same laws apply to the 
human body. 

The mechanics of the living body are, however, quite similar and 
much more important than all the industrial applications which can be 

The three types of levers with the fulcrum in different positions are 
the same in the body (Fig. 2) as they are in general mechanics. A 
knowledge of the exact points where stress and pull are applied, with a 
consequent ability to "figure out" where new growth-structures will 
develop, is of prime importance in broken, misplaced, and re-set struc- 
tures, if the patient is not to suffer untold agony and sorrow in future 

In this connection, the laws governing pulleys, the combination of 
rolling and sliding movement of joints, as well as the principles of 
gravity, must be thoroughly understood ; for, it is simply and solely on 
these principles that the various movements of the body can take place, 
and consequently, it is only a knowledge of such principles which can 
in turn make possible the correction of abnormalities of joints. 

The principles governing friction are applied in the correction -of 
both internal and external injuries, while experimental physiology would 
be impossible without a knowledge of centripetal and centrifugal forces 
and the laws governing liquid and gaseous pressures. 

The laws governing liquids apply throughout the entire body in 
great detail, for there is scarcely a spot as large as the point of a needle 
in the body that liquid nourishment (blood or lymph) does not enter. 
Pressure in any region causes swelling, varicose veins, dropsy, and a 
host of other ills ; while bed-sores are nothing more or less than the 
effect of continued pressure of blood in the same vessels of the side or 
back on which the person lies, gravity causing the blood to sink to the 
lowest level and be held there. 

An understanding of the difference in densities makes possible many 
physiological experiments, which w r ould otherwise result fatally to the 
patient. A solution, if it is to be injected, must not only have the proper 
density so as not to cause a too rapid change in the blood, but the whole 

38 General Biology 

subject of osmosis, diffusion, and capillary attraction must be under- 
stood before such an experiment can be intelligently applied. 

The place where parasites are most likely to lodge, is largely deter- 
mined by the rapidity, direction, and pressure of the blood-stream. 

Hydrometers and urinometers for testing liquid densities are built 
on the principles just enumerated. 

Air is a gas, and as such comes under the laws governing gaseous 
pressure and gaseous diffusion. When it is remembered that the whole 
process of life is snuffed out when the breathing apparatus ceases to 
work properly, it will be seen that the aeration of the blood to keep it 
red and healthy, the working of the lungs under normal and abnormal 
conditions (the latter in chest puncture), the being overcome by gas, 
externally or internally, as well as the changes in breathing at different 
altitudes and at different depths (as on mountain-tops and in subma- 
rines) ; all these can only be understood and helped by a thorough study 
of the laws *and principles applying to gasses. 

The principle of the force-pump makes the pumping of the heart 
and the one-way valves in the heart and veins understandable. 

All food eaten can only be reduced to blood by a burning process, 
called oxidation. Unless the principles governing heat are understood, 
the processes of digestion and the consequent abnormality — indigestion 
— must go on unremedied. 

The principles of ventilation in the home, office, work-shop, or sick 
room, make for health or disease, just as one applies them or leaves them 
unapplied. A window opened at the top warms the incoming air before 
it strikes the patient. The knowledge that warm air ascends and cold 
air descends suggests that a heating plant must be placed in the base- 
ment and a cooling plant in the attic. The principle of evaporation 
explains how outpourings of the sweat glands, by being drawn off 
rapidly into the surrounding atmosphere, make it possible for warm- 
blooded animals to retain an even temperature, regardless of varying 

In "chills" the body really produces more heat than ordinarily, but 
it is the heat-regulating apparatus which is out of order. 

Thermometers and hygrometers are measuring instruments by 
which we note the amount of heat and moisture respectively in the 
atmosphere. They are, of course, simply applications of laws learned 
in physics. 

Then, too, boiling and sterilizing make food, which is normally un- 
palatable and sometimes even injurious, palatable and non-injurious. It 
is sterilization also which makes antiseptic surgery possible. 

The laws governing liquids under varying conditions of heat give 
us the basis for understanding evaporation, condensation, distillation, 
conductivity, convection, radiation, and even plumbing and heating. It 
explains why germs can be killed at a much lower temperature when 
there is moisture in the air (steam) than otherwise. In fact, a human 

Co-ordination of Subjects 39 

being can live in a boiling-point temperature if the air is dry, but he 
cannot live in anywhere near so high a temperature if there is moisture. 

The entire understanding of the working of the ear is a matter of 
physics, in that "sound" is a branch of that science. And, as the larynx 
is the instrument through which our vocal sounds are produced, this, 
too, must be studied in the light of physics. 

All knowledge of the eye, such as our ability to fit glasses, opera- 
tions for ocular defects, and all the instruments with which the modern 
oculist examines and remedies eye-troubles, are the result of direct 
applications of the principles of "light," which, like "sound," is a branch 
of physics. Any assistance in improving hearing or sight must, there- 
fore, be looked for only in the laws of physics. 

The microscope, without which practically none of our modern 
scientific work would be possible, is the direct application of the laws 
found in physics, and there cannot be a single improvement in that 
instrument until a new principle of physics is discovered. 

Likewise, the microtome, the instrument by which we are able to 
cut minute sections for the microscope, could not cut with precision the 
thin slices that it does (1/25,000 of an inch in thickness), if it were not 
made in accordance with the laws of physics. 

Electricity, used so much now in the treatment of disease, the x-ray, 
the fluoroscope, and radium — all these come under the science of 

That same science explains why the blood-platelets gather along 
the blood-vessel where the blood stream is slowest; it explains how 
coagulation is thus assisted so that we do not bleed to death when 
wounded; it tells us. why one can crawl over thin ice when walking 
across the same ice-sheet would be impossible ; why we can safely crawl 
on the floor in a room filled with smoke, when standing erect would be 
fatal; it makes an intelligent understanding possible of how to drain 
wounds ; it tells us why water-pipes burst when the water in them 
freezes; it tells us why a quilt or comforter of cotton is warmer than 
a woolen blanket; it tells us why men's voices are different from those 
of women's, and why the pupil of the eye can accommodate itself to 
changing distances and intensity of light. And, just as it tells us that 
an electric bell will not ring until the proper connection is made, so 
it makes possible the locating of lesions in the body by noting where 
nerve connections are functioning properly and where they are not. 

Probably the mathematical sciences may seem somewhat remote 
from the study of life in general, yet calculus is needed in the study 
of physical chemistry, and the laws of refraction in the fitting of glasses. 
The relationships of structure in the body must be studied both as to 
their quantity and quality. The various names given to the different 
forms and shapes of the parts of the body are largely taken from 

Surely so remote a subject as ancient Greek is far removed from 

40 General Biology 

modern scientific study, and yet the student need but turn to the 
glossary of this book, and go over the' names there given, to see that 
ancient Greek is not only valuable, but essential ; for, practically every 
name of plants and animals comes from the Greek, and unless the 
meaning of the word itself is known, the entire subject-matter becomes 
mere memory work. 

The reason each student must draw a picture of what he sees in 
his laboratory experiment, is to force him to observe so well and so 
accurately that he can make so accurate a drawing of a structure that 
another may in turn recognize the object from the drawing. Drawing 
a picture of what he sees also forces the student to keep the subject 
in mind for a greater period of time than would otherwise be the case, 
and gives him a definite graphic mental picture of what he has seen. 

A knowledge of English makes it possible for the student to present 
a word-picture of the same matter that the drawing presents. 
A description is, therefore, demanded of the student in addition to the 
drawings, thus again causing him to call to mind all that he has seen 
and noted. This not only means that the repetition will cause him to 
remember the subject-matter the better, but it means that he learns to 
do that particular thing upon which much of his future reputation as 
a professional man depends, namely, to prove to others in clear and 
telling language what he knows. 

The mere gathering of facts is of no more value than the mere 
gathering of bricks. The important thing in science is to be able to 
coordinate the facts one finds, and to read into these facts their real 
meanings. Meanings, however, require the use of the intellect, and the 
laws which govern the intellect are embodied in that branch of study 
called philosophy. The most important philosophic studies for the 
scientific student are logic, psychology, and ethics. 

Every valid conclusion which anyone may form must be built up 
logically. Logic is merely the grammar of reason. In fact, every 
diagnosis that a medical man makes, must be built entirely upon logic 
if it is to be worth anything, or to stand the test of truth. 

The study of the way in which the mind works is called psychology, 
and a man cannot intelligently study and clearly understand any of the 
abnormal workings of the human mind, unless he first knows the normal. 
He can know little about mental or nervous diseases unless he knows 
the way in which the mind works when it is not diseased. In his study 
of neurology the medical student follows the various nerve-tracts of the 
brain and spinal cord, but he cannot understand the real meaning of 
these nerve-tracts unless he knows the principles of psychology. He 
will become a follower of fads and fancies while he misses the under- 
lying truths and facts which the real scientific man should have. 

From the philosophical realm we obtain the validity of our ethics. 
Ethics is the science of conduct. We know that holding an air-breathing 
animal under water will drown it. And just as death to the animal 

Co-ordination of Subjects 41 

follows such an act, so, too, many of our acts bring a definite punishment 
of some kind with them. It is to know what acts bring punishments, 
so as to know what acts to avoid, which is the distinct province of 
ethics. In other words, it helps us to arrange a definite "philosophy of 
life" for ourselves. 

And lastly, one or two modern foreign languages should be known 
in order that we can the better obtain various angles and other points 
of view, for there are many possible explanations that the same facts 
may seem to prove. One has but to read through any ordinary textbook 
of science to find quoted there an overwhelmingly large number of 
foreign names and papers. This means that no one can deem himself 
a master of his subject unless he knows at least many of the thousands 
of observations which have been made by the great scientific minds 
of other lands. Unless he knows this, he is bound to spend a large part 
of his life in the attempt at proving or disproving many things which 
have already been proved or disproved by others. He is wasting the 
time which should be given to more valuable work. 

From what has been said above it will be seen that practically all 
the sciences must be studied to throw light on the different workings 
of the body. 

At this point it is necessary for the student to grasp the fact that 
every living thing must be considered as a complete unity, and that 
every organ and every part of an organ which a living thing possesses, 
is definitely connected to, and with, every other part of the body. 

One may suffer from headaches, or eye-trouble caused by displaced 
bones in the feet, which in an indirect way press against nerves con- 
necting with the head ; or, one may have a backache or earache, or even 
rheumatic difficulties, due to ulcers beneath the teeth. 

It is for reasons such as these that it is necessary for the dentist, as 
well as the oculist, to study Biology, and to learn the unity of the living 
being. For there is no more reason for a student of dentistry to confine 
all his study to the teeth alone, or an oculist to the eye alone, than it 
is for a nerve specialist to study the nerves alone. Any such one-sided 
study leaves out of consideration the most important factors necessary 
to a legitimate diagnosis. And, with a wrong diagnosis, the treatment 
is bound to be wrong, or at most, mere guess-work. 

It is well also for the student to bear in mind that, though he may 
not immediately see the relationship of some things to the general 
course he is taking, it does not follow that such relationship does not 
exist. One can learn to start and stop a locomotive in twenty minutes, 
but this does not make one an engineer. It takes years to do this. It 
is not when all things go well that the expert is called in, but when 
things go wrong. This is just as true of the engineer as it is of the 
physician, the dentist, the lawyer, and other professional men. And 
it is only he who knows the relationship of all the parts, who can hope 
to become an expert. 

42 General Biology 

In conclusion, the student should remember that college courses 
are arranged on a minimum basis. That is, the work laid out for the 
student is the least amount of work he can do and yet obtain a passing 
grade. It is, therefore, only the student who actually does more than 
is required, who deserves any credit worth mentioning. 



THE frog lends itself to laboratory work in Biology probably better 
than any other animal. It is sufficiently common to be somewhat 
familiar to the student, and it can be obtained practically at any 
season of the year. It is a vertebrate (Latin — vertebratus=jointed), 
which means it has a back bone, and an amphibian (Greek — amphi= 
both-(-bios=:life), meaning that it lives a double life. This latter state- 
ment refers to the animal's inability to live either on land alone, or en- 
tirely submerged in water. This inability to live entirely in the air or in 
water is well shown by the fact that, if the frog's skin becomes dry, as it 
does when the animal is away from water and in a dry atmosphere, the 
animal dies, because the skin is then no longer capable of serving as 
an organ of respiration (L. re=back-|-spira=breathe). Contrariwise 
if it be constantly immersed in water, it will also die, because it must 
breathe air. 

The particular species (Rana pipiens) that we are describing 
(though any other of the common forms would answer the same pur- 
pose) is found in or about fresh-water lakes, ponds, or streams. The 
species is fairly well distributed over the entire North American con- 
tinent, except the Pacific slope. 

Everyone has noticed the longer and stronger hind legs of the frog, 
and the squatting position it assumes on land, as well as the rapidity 
with which it leaps into the water when disturbed along the banks. 
If one observes if while in water that is beyond its depth, it will be 
noted that the hind legs hang out straight and the tip of the nose is 
exposed to the air. Should it be disturbed while in this position, the 
hind legs are flexed (L. flecto=bend), which throws the body downward. 
The fore legs are used in arranging the direction in which the animal 
will go; the hind legs are then extended (L. ex=out-ftendo=stretch), 
completing the movement which forces it forward. 

Everyone also knows the sound of croaking frogs at night, 
especially when the atmosphere becomes damp, though it is not so gen- 
erally known that the frog croaks far more frequently during the 
breeding season than at other times. The croaking can be accomplished 
both in and out of the water. The croaking under water is produced 
when the air from the lungs is forced past the vocal cords into the 
cavity of the mouth, and then back again into the lungs. 

There is another reason why the frog may be considered as leading 
two lives, (Fig. 3) beside the fact that it needs both air and water, and 
that is that it lives a different type of life when young than when grown. 
This comes about as follows : The eggs of the female frog are prac- 


General Biology 

tically always laid in water and hatched there. Little tadpoles develop 
from these eggs and breathe by gills in the larval ( ) 1 condition. 

Some species of frogs retain these gills all through life, even though 
lungs may be present in the adult forms. The tadpole gradually develops 
into the mature frog, losing its tail and developing the long hind legs 
and the short fore legs so familiar in the adult animal. 


It is essential that one examine quite carefully the external struc- 
ture of any plant or animal one may wish to study; for, unless this 
knowledge is borne in mind, internal structure cannot be interpreted 
correctly. It is well also to keep in mind our own bodies, and to observe 
similarities and differences wherever they may occur in animals and 

C, egg con- 
4, eggs before B, eggs after they taining young 
they are laid are laid tadpole 

D, young tadpoles attaching 
themselves to a plant 

B. young tadpole with ex- F, young tadpole with 
ternal gills internal gill3 

G, young tadpole with hind lega 

H, tadpole with webbed 

I, tadpole with legs and arms 

J, young frog 

Fig. 3. 

Eggs, Tadpole, and Adult Stages of Frog. 
(After Brehm and other authors.) 

It will be noted immediately, that the frog has no neck. The head 
is broadly united to the trunk. The eyes protrude somewhat, but can 
be withdrawn readily into the orbits. A pressure put upon the eyes, 
when the mouth of a frog is open, will extend the inner membrane lining 
of the roof of the mouth quite prominently, showing that the orbit, or 
eye socket, is not separated from the mouth by any bones of the skull 
as in man. The dark oval opening of the eye, the pupil, is surrounded 
by the iris, a more brightly colored ring. There are upper and lower 
lids, the upper one moving but slightly, the lower one thin and trans- 
parent, and capable of covering the entire eye. This lower eyelid is 
different from that of most animals, and this type of lid will be met with 
again in other animal-forms to be studied. The nictitating membrane 
( ) is separated from the lower lid (Fig. 4), but 

1 The empty parentheses are to be filled by the student, with the derivation of the word as found 
in the Index-Glossary. 

The Frog 


appears to form a continuation. In birds, for example, this membrane is 
also very thin and can be thrown over the eye from the inner angle of the 
orbit. Behind the eye is a more or less circular area called the tympanic 
membrane, ( ) which covers the ear drum. There 

is a slight prominence in the center of this membrane produced by o?te 
of the small bones called the columella ( ). This 

bone connects with the inner ear, and, when any sound-wave strikes the 
tympanic membrane, the vibrations are communicated through this bone 
into the internal ear. This gives rise to the sensation of hearing. On 
the inner side of the tympanic membrane we find a little cavity known 
as the Eustachian tube ( ), which opens internally 

into the mouth. There is no external ear as in man. 

The two openings immediately 
above and behind the tip of the nose 
are called nostrils or external nares. 
Sometimes in front of the eyes there 
is a little light area known as the 
brow-spot. This was connected 
with the brain in the embryo 
( ). The brow-spot 

is a feature of considerable interest 
from the fact that in the embryonic 
development of the frog, it connects 
with a peculiar outgrowth of the 
brain known as the epiphysis 
( ) or pineal gland. 

This is supposed to be a rudiment 
( ) of a stalk 

which formerly connected with the 
medial eye ( ) 

which still persists in certain forms 
of reptiles (Fig. 5) ( ). 

The nostrils are guarded by valves 
which open and close during respi- 

The mouth extends from one 
side of the head to the other, and the 
anus ( ) is situated 

) end of the body. The fore limbs 
are divided into an upper arm, a fore arm, and a manus, ( ) 

or hand, the latter possessing four digits and the so-called thumb, a 
rudiment of the fifth. In the male the inner digit is thicker than the 
corresponding one of the female, especially during the breeding season. 
The entire fore arm is also relatively thicker in the male than in the 

The hind limbs are well adapted for jumping and swimming These 



4. Examples of Nictitating Membranes. 
(From various authors.) 

at the posterior ( 


General Biology 

are divided into three portions. The upper portion is known as the 
thigh; the middle, the crus or shank; and the distal ( ) 

portion, the foot or pes. The foot, which is well developed, has five 
toes and the rudiment of a sixth, called the prehallux ( ), 

situated on the inner side of the foot. The toes themselves are con- 
nected with a web, making the foot quite efficient as a swimming organ. 
There are also small cushions, called subarticular pads, ( ) 

between the bones of the toes. 

Fig. 5. Pineal eye of a Lizard; diagrammatic. A brain and upper wall of the 
skull, the latter cut through; B, pineal eye alone, in section. V, Z, M, H, cerebrum, 
thalamencephalon, optic lobes, cerebellum; h skin, ^ roof of skull, o unpigmented 
portion of skin below which the pineal eye lies in a hole in the roof of the skull; 
p epiphysis, i hypophysis, 2 optic nerve. L lens, R retina, N nerve of pineal eye. 
(After Boas.) 

The skin is smooth and loose, containing large black pigment spots 
( ) and some green and golden pigments as well. 

As with other vertebrates, the skin has two layers, an outer called the 
epidermis ( ) and an inner, the dermis ( ). 

Nothing similar to hair or scales can be found on the frog. In the skin 
there are large mucous glands ( ) which keep the 

surface slimy, and there are also some poison glands secreting 
( ) a whitish fluid, supposedly for defensive pur- 

poses. Behind the eyes there are usually two light colored ridges, 
formed by a thickening of the skin and called the dorso-lateral dermal 
plicae ( ) or folds. There may be some smaller, 

irregular, longitudinal folds ( ) of skin between 

these. It will also be observed that the color of the skin is much darker 
on the upper, or dorsal, surface than below, where it is almost white. 


As with man, the various organs ( ) and tissues 

( ) of the frog's body are supported by an internal 

skeleton of bones. This is called an endoskeleton ( ) 

to distinguish it from the skeletons in such types of animals, as the 
crayfish, which have their entire skeletal structure on the outside of the 
body, forcing that animal to grow an entirely new skeleton whenever 
the animal itself grows larger than its skeleton jacket will stretch. The 
higher forms of animals all have endoskeletons. The different parts 

The Frog 47 

of the body are moved by the action of muscles, which in turn are 
innervated ( ) by nerves. To know the internal 

structure of an animal one must know all that can be known in regard 
to the following systems : 

1. The Digestive System. 

2. The Circulatory System. 

3. The Respiratory System. 

4. The Excretory System. 

5. The Nervous System. 

6. The Skeletal System. 

7. The .Muscular System. 

8. The Reproductive System. 

After an incision is made along the mid-line (Fig. 6) of the ventral 
( ) surface of the animal from the lower angle of 

the jaw to its most posterior end, and the skin-coverings are pulled aside, 
the internal organs are seen. These are called the viscera ( ). 

The cavity in which they are found is known as the coelom, ( ) 

or body cavity. 

If the animal has just been chloroformed, the heart will still be 
beating. The heart is contained in a sac-like structure called the 
pericardium ( ) . 

Surrounding at least a portion of the pericardium, are three promi- 
nent lobes of the reddish-brown liver, while the lungs, looking like small 
strawberries, lie, one on each side, near the anterior end of the abdomi- 
nal cavity. 

The stomach and the coiled intestine attached to it, are easily recog- 

The kidneys are flattened reddish bodies attached to the dorsal body 

If it is the breeding season, and the frog is a female, almost the 
entire body-cavity may be filled with thousands of eggs. The eggs 
in turn are contained in a film-like covering known as the ovary 
( ) and oviducts ( ), the latter 

organs serving as tubes through which the eggs leave the body. If 
the specimen is a male, the two testes ( ) will be 

suspended by little membranes at the side of the digestive canal (t, Fig. 
6). The entire lining of the abdominal cavity in all the higher forms 
of animals is called the peritoneum ( ). When one 

or two layers of this peritoneum suspend, or hold up an organ, such as 
the digestive canal and the reproductive organs, such suspending peri- 
toneum is called a mesentery ( ). 


It will be noticed that the tongue is extensile ( ), 

that is, it can be thrown forward and outward. On the tongue there 
is secreted a sticky substance which causes objects with which it comes 


General Biology 

in contact to adhere. It is interesting to know that unless an object 
is moving, the frog pays no attention to it. The mouth or oral opening 
is relatively large. The opening on the interior is called the buccal 

Fig. 6. A Male Frog Dissected from the Ventral Side. 

a.ab.v., Anterior abdominal vein, cut short, ligatured, and turned back, a.musc, 
cut edge of abdominal muscles; bl., urinary bladder; c.d., common duct of gall- 
bladder and pancreas;, dorsal aorta;du., duodenum; f.b., fat body; jem.v., 
femoral vein; g.b., gall-bladder; lit., heart; hy.n., hypoglossal nerve; im., ileum; 
i.v.c, inferior vena cava; k., kidney; k.d., kidney duct with vesicula seminalis; 
lr., liver; a., point at which c.d. enters the duodenum; pes., pancreas; pl.v., pelvic 
vein; r.L, right lung; rm., rectum; r.p.v., renal portal vein; sar., sartorius muscle; 
sm., mylohyoid muscle; sp., spleen; st., stomach; t., testis; v. v., vesical vein. (After 

( ) cavity. There are teeth on the maxilla ( ), 

premaxilla ( ), and vomer bones ( ). 

These assist in holding, but not in masticating the food. Immediately 

The Frog 


back of the tongue on the floor of the mOuth is a narrow slit called the 
glottis ( ) leading to a tube 1 passing to the lungs, 

and directly behind the glottis, a larger opening is found, leading to 
the oesophagus, which empties into the stomach. The stomach itself 
is crescent-shaped, lying mostly on the left side of the body. The 
larger anterior portion is called the cardiac end ( ), while 

the constricted or posterior portion, meeting with the intestine, is known 
as the pyloric ( ) end. 


I. m. 

A. A Diagram of a Transverse 

Section Through the Ileum 

of a Frog. 

cm., Circular muscle layer; c.t., 

submucosa; ep., epithelium which 

lines the gut; l.m., longitudinal 

muscle layer; msnt., mesentery; 

per., peritoneum; rid., longitudinal 

ridges of ileum composing mucosa. 

Fig. 7. 


B. A Portion of the Section Shown 
in A, More Highly Magnified. 
b.v., Blood vessel; c.t., connective 
tissue of mucous membrane or sub- 
mucosa; cm., circular layer of mus- 
cle fibres; ep., epithelium; g.c, 
goblet cell; l.m., longitudinal layer 
of muscle fibres; let., "lacteal" or 
lymph vessel of the intestine; leu., 
leucocyte or lymph corpuscle; p.e., 
peritoneal epithelium. (After 


The first portion of the intestine, a sort of U-shaped band, is known 
as the duodenum ( ). The several coils following 

it are the intestine proper. This intestine finds its way into a large, 
short chamber known as the rectum, which in turn communicates with 
the exterior through what is called the cloacal opening ( ). 

The walls of the stomach are composed of five layers (Fig. 7), the outer 
portion quite thin, called the peritoneum; then two muscular layers, the 
outer called the longitudinal, and the inner the circular muscle layer, 
followed by a spongy division called the submucosa and an inner folded 
mucous layer, the mucosa itself. This latter is made up of glands lying- 
in connective tissue. These glands are longer at the cardiac than at the 
pyloric end. The inner layer of the intestine, the mucosa, is considerably 
folded and consists of absorptive and goblet cells. The urinary bladder, 
the reproductive ducts, and the rectum open into the cloaca. 

^This tube to the lungs is a part of the respiratory system; consequently the opening, the glottis, 
really does not belong to the digestive system, but it is mentioned here because the student will see it 
while noting the surrounding structures and it is well for him to know all related parts of a 
given region. 


General Biology 

The digestive glands themselves are the pancreas and liver, the for- 
mer lying immediately between the duodenum and the stomach. The 
pancreas is a much branched tubular gland, secreting an alkaline diges- 
tive fluid. It empties into the common bile duct. The three-lobed liver 
also secretes an alkaline digestive fluid, known as bile. This is carried 
by the little bile capillaries into the gall bladder where it is stored until 
food enters the intestine, when it passes into the duodenum through 
the common bile duct. Digestion begins in the stomach. 

According to Latter, "the alkaline fluid secreted by the mucosa 
layer of the oesophagus and the acid gastric juice secreted by the 
glandular walls of the stomach digest out the proteid portion of the food 
by means of a ferment, ( ) called pepsin, which changes 

proteids into soluble peptones. The food then passes through the pyloric 
constriction into the intestine. Here it is attacked by the pancreatic 
juice and the bile. The pancreatic juice contains three ferments: (1) 
trypsin, which converts proteids into peptones ; (2) amylopsin, which 
converts starch into sugar; and (3) steapsin, which splits up fats into 
fatty acid and glycerin. The bile emulsifies fats and converts starch into 
sugar. The intestinal wall produces a secretion which probably aids in 
converting starch into sugar. 

"Absorption begins in the stomach, but takes place principally in 
the intestine. The food substances, which have been dissolved by the 
digestive juices, are taken up by the mucosa layer, passed into the blood 

Right lobe, 


Subvertebral \ Subcutaneous 
lymph smus t ; lyr, ' 

■Left lobe, of limr 

ranch qfant. 
abdominal to 
portal vein 

Qall bladder' 

Anterior / 
unal vein 

Portal vein 

Postcaval win, 




Fig. 8. 

Muscles (fabdomen^ i<:Cl: ^xx^±?iX^ :i ^ '^^ n 
Parietal \ p£n£owum 
""■B ~ Abdominal vein 

Diagrams of Important Relationships. 

A. The relation 
pancreas and liver. 

B. Diagrammatic 

of the hepatic portal system to the stomach, intestine, 

transverse section through the abdominal region of a frog. 

C. Diagram of the two main channels by which food enters the general circula- 
tion in mammals, e, intestine with villi; r a, right auricle of the heart; m, post- 
caya; n, precava; o, thoracic lymph duct; p, pancreas; q, pancreatin duct; s, portal 
vein; t, bile duct from /, liver; arrows indicate the course of secretions entering the 
intestine, and of the absorbed food departing therefrom. 

(A, after Howes; B, after Parker; C, from Needham's General Biology, by 
permission of The Comstock Publishing Co.) 

and lymph, ( ) and are transported to various parts 

of the body (C, Fig. 8). The undigested particles of food pass out 
of the intestine into the cloaca and are then discharged through the anus 
as faeces." 

The absorbed food is used by the frog to build up new protoplasm 

The Frog 51 

to take the place of that consumed in the various life activities, and to 
increase the size of the body. Food is stored up in the liver-cells as 
glycogen, a carbohydrate similar to starch and often called "animal 
starch." The absorbed food is conveyed to the liver by the portal vein 
and is there converted into glycogen, pending the demands of the gen- 
eral tissues of the body. As occasion rises, it is converted into more 
soluble material, a sugar, and sent into the main bloodstream via the 
hepatic veins and inferior vena cava. Fat globules are also contained 
in the liver cells. The storage function of the liver is one of considerable 
importance, especially during hibernation and in the breeding season ; 
the weight of the organ exhibits a well-marked seasonal variation in 
accordance with the amount of reserve food contained. The details of 
this phenomenon have been worked out by Alice Gaule in Rana escu- 
lenta. The breeding season of this form is in May, June, and July. 
The table shows the average weight of the liver in the two sexes month 
by month. 

"It will be observed that the liver is most depleted in both sexes 
in June, the middle of the breeding season, and that it reaches its maxi- 
mum weight in September when the system has recovered from the 
exhaustion of spawning. Throughout the winter the reserves are being 
steadily used up, with no recovery by the female, the average weight 
of whose liver is greater than that of the male, but with a slight recovery 
in March and in May by the male. It is probable that this general 
difference depends upon the fact that the ovaries of the female make a 
great and continuous demand upon her system throughout the whole 
period of maturation, so that in spite of renewed feeding in the spring 
there is no recuperation in the liver. In the male, however, there is no 
such continuous drain but rather a sudden call upon the reserves at the 
actual time of pairing — a call due not only to the discharge of the 
spermatozoa but also to the muscular exertions of the male at that 
season. This call is marked in vigor by the sudden reduction of the liver 
to rather less than half its weight in June. 


Weight of 
male liver 

Weight of 
female liver 




10 grms. 



13 grms. 




















52 General Biology 

"Reserves of food are also laid up in the fat-bodies. These have no 
direct connection with the digestive system, but may conveniently be 
dealt with here. They are bright yellow, finger-like bodies grouped in 
front of the testes or ovaries as the sex may be. They develop from 
the anterior portion of the genital ridges whose posterior portions alone 
give rise to the sexual organs. In the autumn they are of great size and 
loaded with fat-cells, a certain amount of lymphatic tissue being also 
present. In the spring they are much reduced. It is probable that they 
also perform other functions at all seasons of the year, but on this point 
we have no precise knowledge." 


Glands may be conveniently classed into two groups : 

Exocrine glands, that is, glands whose product are used externally 
or on substances entering the body, and which generally leave by way 
of ducts. 

Endocrine glands, that is, glands whose products act on the body 
itself, not on substances brought into it. This type of gland generally 
has no duct; or if so, as in the case of ovaries and pancreas, the 
"endocrine" portion of the secretion is absorbed by the blood vessels 
and does not leave the gland by way of a duct. The term "ductless 
glands" has been used to designate these glands, but has been found 
inappropriate. The products of the endocrine glands are known fre- 
quently as "internal secretions," and are composed of active agents simi- 
lar to enzymes. The name of "hormone" (excitant) has been given to 
these agents, which differ from enzymes primarily in that their activity 
is not destroyed by boiling. 

It has been found, however, that the action of the endocrines may 
be both stimulatory and inhibitory, as, for instance, in certain experi- 
ments on tadpoles which were fed with thymus and thyroid gland. 
Gudernatsch (1912-14) found that the thyroid food stimulated develop- 
ment and inhibited growth, while thymus stimulated growth and 
inhibited development. Thyroid-fed tadpoles matured in four weeks, as 
contrasted with the normal period of twelve weeks, but were dwarfs and 
pigmies in size; while thymus-fed tadpoles were gigantic in size, but 
after sixteen weeks showed no indication of transformation, in fact, had 
not yet developed their hind legs. From certain other experiments on 
the sexual glands, it has been similarly concluded that the internal secre- 
tion from the sex glands (specifically that of the interstitial cells) acts 
both as a stimulant to the body so that it will develop the characteristics 
pertaining to its proper sex, and as an inhibitor in suppressing those of 
the other sex. The excitant has been named hormone; the inhibitor, 

The products of the various endocrines are regulatory in nature, and 
control or affect such processes of the body as growth, puberty, sec- 
ondary sexual characters, blood pressure, metabolism, distribution and 

The Frog 53 

concentration of substances, muscle tone, blood sugar, etc. Instincts, 
emotions, mental and psychic states are stimulated, inhibited and com- 
plicated by endocrine action. 

The two thyroid glands are situated on either side of the hyoid, and 
secrete quite a quantity of iodin. In man, their atrophy is associated 
with the disease called cretinism ( ) where certain 

parts of the body, such as the head, may become very large. Cretins 
are almost always idiots. 

The two thymus glands ( ) lie one behind each 

tympanum. They are small and oval in shape, usually reddish in color, 
and are placed directly beneath the depressor mandibular muscle. The 
thymus, like the thyroid, diminishes in size with age. 

The adrenal bodies ( ) are little bands of a 

yellowish color extending along the mid-ventral surface of the kidneys. 
They secrete adrenalin, a substance necessary for the life of the animal. 
This substance is used to a considerable extent in medicine at the present 
time as it will cause a contraction of the blood vessels and raise the 
blood pressure after injection. However, a little later a reaction sets 
in, and a lowering of blood pressure follows. 

The spleen ( ) is a reddish organ lying imme- 

diately dorsal to the anterior end of the cloaca. It is supposed to act as 
a sort of filter for the blood. The old corpuscles are destroyed and new 
colorless ones are formed. It must be remembered that all that is known 
in regard to the ductless glands demonstrates that they are of vital 
importance, but that no absolute conclusions can be drawn as to definite 
functions of any of them ; for, while one or two of their functions are 
known, there are probably many more functions that are not yet 
dreamed of. 


It is essential that the student grasp the fact that there are several 
types of circulation. The systemic proper is that closed system of blood 
vessels by which the blood leaves the heart and passes through the large 
arteries into the capillaries to carry nourishment to every point in the 
body (Fig. 9). These arterial capillaries then meet with the venous 
capillaries, and waste-matter is collected in the blood and carried by the 
veins into two anterior and one posterior venae cavae by which the blood 
is returned to the heart. 

The heart itself, however, must have blood vessels carrying nour- 
ishment to the heart-walls just as an engine run by steam and supplying 
water to different parts of a building, must have water supplied to its 
own boiler in order that the steam, which gives the engine its power, 
may continue to be generated. 

The heart muscle, which is the engine of the body, must similarly 
have a supply of blood to its own walls in order that the heart may 
be able to pump the blood to all parts of the body after it has entered 
the heart from the lungs where it was aerated. The blood sent to be 


General Biology 

aerated forms the second type, or pulmonary circulation. The digested 
food which the individual has absorbed must now be taken into the 
blood and be made a part of that blood, so that there is a replacement 
of lost substances. This explains why the blood, which goes to the 
digestive tract by the coeliac axis, passes through two series of capillaries 
before returning to the heart : 



Fig. 9. Diagram Representing the General Course of Blood in the Frog and the 
Principal Sets of Capillaries (cp) Through Which the Blood Flows. 

The vessels through which impure blood goes are dark, while those carrying 
pure blood are left unshaded. The arrows indicate the direction of blood flow. 
ant. ab, anterior abdominal vein; ao' , aorta; au' , right auricle; au", left auricle; 
c.c, common carotid artery ;cce, cceliaco-mesenteric artery; cp.a, anterior systemic 
center;, alimentary center;, cutaneous center; cp.hp, hepatic center; 
cp.p, posterior systemic center;, pulmonary center;, renal center; cu, 
great cutaneous artery;, dorsal-aorta; l.h' ', anterior lymph heart l.h" ', posterior 
lymph heart;, musculocutaneous vein; p. hepatic portal vein;, pulmo- 
cutaneous vein; pr.c, precaval vein; pt.c, postcaval ve'm;pul, pulmonary vein; 
re, renal artery; rp, renal portal vein; s.v., sinus venosus; tr.a, truncus arteriosus; 
v, ventricle. (After Howes.) 

First, into the capillaries of the intestine where it receives the 
nutriment absorbed from the food. Then, after being collected into the 
large portal vein, it enters the liver. 

Second, after entering the liver, the portal vein breaks up into 
another system of capillaries within that organ. 

After the blood has passed through the liver, this second set of 
capillaries unites to form the hepatic vein which empties into the large 
posterior vena cava leading to the sinus venosus. This whole system, 
where veins break up into capillaries but are again united to form a 
second vein, is called a portal system. 

Part of the blood which goes to the legs also has a double system. 
First it enters the capillaries in the leg muscles. Then on its way back 
it passes through the kidneys where it is broken up into capillaries. 
The blood which takes this route returns from the leg through the renal- 
portal vein, while the rest of the blood from the legs is diverted to the 
abdominal vein which passes through the liver (but not the kidneys) 
on its way to the heart. 

Now, just as the heart must have an arterial supply of blood to 

The Frog 


its own walls in addition to that which it pumps from its cavities, so 
the liver and kidneys must also have their own supply of blood to feed 


Fig. 10. The Frog's Heart. 

A, seen from the ventral side; B, from the dorsal side; C, heart opened and viewed from ventral side. 
(The ventral wall of the truncus, ventricle, and auricles has been removed.) 

A. c.a, carotid arch; car, carotid artery;, carotid gland; I. a, lingual artery; 
pea, pulmocutaneous arch; pm, pericardium;,, right and left auricles; 
s.v.c, superior vena cava; sy.a, systematic arch; tr.a, truncus arteriosus; v, ventricle. 

B. i.v.c, inferior vena cava; p.v., pulmonary veins;,, right and left 
auricles;, opening from sinus to right auricle; s.v.c, superior vena cava; s.v., 
sinus venosus; tr\, branches of truncus cut across; v., ventricle. 

C. au.v., Auriculo- ventricular valves; c.a., carotid arch;, cavum aorticum; 
ch.t., chordae tendineae;, left auricle; o.p.v., opening of pulmonary vein; o.pc, 
opening of dorsal division of synangium, by which blood passes from the cavum 
pulmocutaneum to the pulmocutaneous arch; pc. a., pulmocutaneous arch; r. au., 
right auricle;, sinu-auricular opening with valves; si., first row of semilunar 
valves; si'., semilunar valves of second row; sl'.l, the semilunar valve from which 
the spiral valve starts; the line points to a small portion of the valve which has 
been cut open; si'. 2, small semilunar valve at end of cavum pulmocutaneum; si'. 3, 
a small part of a large semilunar valve, of which the rest extends across that por- 
tion of the front wall of the truncus which has been removed; sp.v., spiral valve; 
sy.a., systemic arch; tr.a., wall of truncus arteriosus; tr'., one of the two bundles 
of arteries into which the truncus divides; v., ventricle, (Redrawn from Borradaile.) 

56 General Biology 

the liver and kidney substance, in addition to that received from their 
respective portal veins. 

All the blood coming from the heart, and passing directly back to 
the heart, whether it flows through the portal, renal-portal, abdominal 
or other veins, is classified as the systemic circulation. This is to be 
distinguished from the pulmonary circulation, which deals with the 
blood which, having been returned by the veins to the heart, is now 
sent to the lungs to be purified and aerated. This blood leaves the heart 
ventricle through the pulmonary arteries and is returned to the heart 
auricle through the pulmonary vein. 

It is interesting to note that, in the frog, a part of the already-used- 
blood (venous blood), which in the human being all goes to the lung 
through the pulmonary artery, passes through the cutaneous artery, a 
branch of the pulmonary, to the. skin under the arm, where it is also 
purified by the oxygen in the water. It will be remembered that the 
frog needs both air and water for breathing purposes and breathes 
through both lungs and skin. 

The frog's heart is composed of three compartments (Fig. 10), 
instead of four, as in the higher forms of animals. The blood, which 
has been purified in the lungs, flows into the left auricle through the 
pulmonary vein and is thus kept separate from the impure blood in the 
right auricle. But, as there is only one ventricle, and as blood is always 
received by the auricles, and always expelled from a ventricle, the impure 
blood from the right auricle, as well as the pure blood from the left 
auricle, is all emptied into one ventricle so that it is bound to intermingle. 
However, the blood from the right side is a little more impure than on 
the left, because the left side is directly connected with the left auricle 
and it is the left auricle which has the purest blood. The pure and 
impure blood are also kept partly separated by various irregular muscular 
partitions called trabeculae extending through the ventricle. 

The action of the heart is as follows : The two auricles filled with 
blood contract at the same time, thus forcing the arterial blood from 
the left auricle and the venous blood from the right auricle into the 
ventricle. Here the two kinds of blood are kept from mixing by the 
trabeculae just mentioned. At the systole of the ventricle, some of the 
venous blood, which lies nearest the bulbus arteriosus, is first forced 
forward. This blood takes the most direct route through the wide and 
short pulmocutaneous arteries which are practically empty at the time. 
Some of the arterial blood is next forced out through the carotid arches 
to the head region, while the last blood to leave the ventricle is a mixture 
of the remaining arterial and venous blood, which is forced through the 
systematic arches to supply the general body system. 

Blood usually looks red. This is due to the large red corpuscles 
(Gr. erythrocytes=erythros — red+cytos=cell). The redness itself is 
due to haemoglobin, a chemical substance contained within the cor- 
puscles. There are also white corpuscles, called leucocytes (Gr. leukos= 

The Frog 


white+cytos=cell), in the blood. These are often able to force them- 
selves through the walls of the capillaries and then wander about through 
the tissues. In the liquid part of the blood there is still a third type 
of tiny bodies which are called platelets. Of these little is known. 

Beside the arteries and veins there are also the lymph vessels in the 
skin, intestine, and other parts of the body which belong to the circula- 
tory system. The liquid part of the blood in which the corpuscles float 
is known as plasma. When the blood passes into all parts of the body 
to nourish it, some of this plasma finds it way through the little arterial 
capillaries, bathing the intercapillary spaces. This plasma, which has 
left the blood vessel proper to bathe the body tissues, is called lymph. 
The lymph must be gathered again and made a part of the blood, so 
various little lymph capillaries drain the body and pour the lymph back 
into the veins. These lymphatic vessels are very delicate, and must be 
prepared in a special way to be seen. The little open spaces where 
lymph gathers and from which the lymphatics carry it to the veins, are 
known as a lacunae. These lacunae also connect with large cavities in 
the body. 

The lymph vessels in the intestine have a special name, being called 
lacteals ( ). There are also lymphatic glands found 



Fig. 11. Section Through a Lymph Heart. (After Weliky.) 

kl — Tube-like valve at entrance of vein into the heart. 

v — Vein. 

lymph — Lymph-heart. 

in connection with the lymph vessels. In the frog there are two pairs 
of lymph hearts (Figs. 11 and 347) whose contraction propels the lymph 
in its circulation. 

With this in mind, we take up the principal divisions of the circula- 
tory system. 



There is a true heart consisting, however, of only three cavities 
(Fig. 10), two thin-walled auricles, ( ) one on the 


General Biology 

right and one on the left side, and a muscular ventricle. There is also 
a thick-walled tube called the truncus arteriosus ( ) 

arising from the base of the ventricle, and a thin-walled triangular sac, 
the sinus venosus ( ) from the dorsal side. The 

heart is the central pumping station of the entire circulatory system, 
which furthermore consists of all the arteries, veins, and lymphatic 
structures in the body. Arteries always carry blood away from the 
heart ; veins, to the heart. The fibers of the heart muscle run in every 
direction, so that in systole, ( ) that is, when the 

heart contracts, its size is diminished, and the blood in the various cavi- 
ties is forced out ; then in diastole, ( ) when the 
heart again expands, the blood flows into it. The openings of both the 
auricles and ventricles are guarded by valves, little flaps of membrane 
which permit the blood to flow through the opening quite readily, but 
close up when the blood begins to flow backward, as it would be bound 
to do when the ventricle contracts, if the valves did not block the 
passage. The large truncus arteriosus (the proximal portion of 
which is called bulbus arteriosus), has two large branches, called 

Jfch entity 

Membrane (tfente) 

Wedi* ■ 

/Free far Casrvttt/m 

Fig. 12. Femoral Nerve, Artery and Vein o£ Puppy. 

aortae ( ). The truncus receives the blood as it is 

forced out of the heart when that organ contracts. From here it is dis- 
tributed to all parts of the body. The sinus venosus on the dorsal 
surface of the heart is the cavity into which the veins bring back the 
blood from all parts of the body. The sinus itself opens into the right 
auricle and thus receives all the blood which flows back to the heart 
from all parts of the body, except the lungs. 

The Frog 


The blood from the lungs empties into the left auricle by two small 
veins, one from each lung. 


Blood vessels pass to every part of the body. We know they are 
everywhere because one cannot insert the point of the finest needle in 
any part of the body without piercing them, showing they are so close 


Syshmic.a. ^ Mmocuk 

J (aortic) s ^ 

Cutaneous a 



_ carohd 'Occipital <X. 
eous j S gland/ 

Internal carotid 

Common carotid a. 

Occwito -vertebral 
^ artery 


Coeliaco -mesenteric artery 
Dorsal aorld 

Spermatic- a. , 
Testis '' 


rjL -Hepatic a. 

-Coeliac a, 
~" - * Stomach 

w gastric a. 
^ -Jinterior 
mesenteric a. 

- — -Intestine 


% ' arteries 

Fig. 13. The Arterial System of the Frog. 
(Redrawn from Meissner.) 

together that one cannot get in between them. Arteries are always 
relatively thicker- walled and more elastic than veins (Fig. 12). 

The principal divisions of the arterial system (Fig. 13) may be 
summarized as follows : 

60 General Biology 

I. The common carotid ( ) divides into the 
lingual or external carotid, supplying the tongue and neighboring parts, 
and the internal carotid which gives off the palatine ( ) 
artery to the roof of the mouth, the cerebral carotid to the brain and the 
ophthalmic artery to the eye. There is a little swelling known as the 
carotid gland at the point where the common carotid branches. 

II. The pulmo-cutaneous ( ) artery forms the 
pulmonary artery, passing to the lungs, and the cutaneous artery. The 
cutaneous in turn gives off the auricularis ( ) dis- 
tributed to the lower body and neighboring parts, the dorsalis which 
supplies the skin of the back, and the lateralis which supplies the skin on 
the sides. Most of these branches also carry blood to the various respira- 
tory organs, lungs, skin, and mouth. 

III. The systemic arches pass outward, around the digestive canal, 
and then unite to form the dorsal aorta. Each systemic arch gives off 
an occipito-vertebral artery which divides ; one branch, the occipital, 
( ) supplies the jaws and nose; the other again 
divides to form the vertebral which supplies the spinal cord and muscles 
of the body wall ; and the subclavian which is distributed to the shoulder, 
body-wall and arm. The dorsal aorta gives off the coeliaco-mesenteric 
artery. This divides, forming the coeliac which supplies the stomach, 
pancreas, and liver, and the anterior mesenteric, which is distributed 
under the intestine, the spleen, and the cloaca. Back of the origin of the 
coeliaco-mesenteric, the dorsal aorta gives off four to six urinogenital 
arteries which supply the kidneys, reproductive organs, and fat bodies. 
A small posterior mesenteric artery arises near the posterior end of the 
dorsal aorta passing into the rectum. In the female this artery also 
supplies the uterus. The dorsal finally divides into two common iliac 
( ). arteries which are distributed into the ventral 
body-wall, the rectum, bladder, the anterior part of the thigh (here called 
femoral artery), and other parts of the hind limbs (sciatic artery). 

All the arteries finally break up into a vast number of microscopic 
thin-walled vessels called capillaries (Lat. capillus=hair) by which every 
part of the body is reached. 


The veins (Fig. 14) return the blood to the heart by draining all 
parts through venous capillaries. The veins run in the opposite direction 
of the arteries and constantly become larger and larger. It will be noted 
here that the blood vessels form a closed system and the blood that leaves 
the heart returns to the heart without leaving the vessels. The blood 
from the lungs is collected by the pulmonary veins and poured into the 
left auricle while the rest of the venous blood is carried to the sinus 
venosus by three large trunks. There are two anterior venae cavae 
( ) and one posterior vena cava. The anterior venae 

cavae receive blood from the external jugulars ( ) 

which collect the blood from the tongue, thyroid, and neighboring parts, 

The Frog 


as well as from the innominates which collect blood from the head by 
means of the internal jugulars and from the shoulder by means of the 
subscapulars, and the subclavians which collect blood from the fore limbs 
by means of the brachial, and from the side of the body and head by 

Sino- auricular 
opening ~ ' 


R. precaval 

Liver - 

£rternd jugular win 
Innominate vein 
-Subclavian vein 
- -Brachial Vein 

--Hepatic vein 

Musculo - 
'" cutaneous v. 

_ Hepatic 
portal v 

Kidney - - 
Testicle - - 

Abdominal v - - 
'Renal veins - - 

Transverse iliac vein 

^-Postcaval v 

——-Mesenteric v. 

Dorso- lumbar 


Renal portal v. 

—Pelvic uein 
Femoral v. 
Sciatic v 

Fig. 14. The Venous System of the Frog. 
(Modified from Meissner.) 

Note that the blood returning to the heart from the posterior limbs must do one of two things: 
(1) It must pass through the kidney (renal portal system), or (2) it must pass, by way of the 
abdominal vein, through the liver (hepatic portal system). In either case, it enters the sinus venosus 
by way of the postcaval vein, and from there to the right auricle through the sinu-auricular opening. 

means of the musculocutaneous veins. The posterior vena cava receives 
blood from the liver by means of two hepatic veins, from the kidneys by 
means of four to six pairs of renal veins, and from the reproductive 
organs by means of spermatic or ovarian veins. 

62 General Biology 

The veins which carry blood to the kidneys constitute the renal- 
portal ( ) system. The renal-portal vein receives 
the blood from the hind legs by means of the sciatic and femoral veins, 
and the blood from the body-wall by means of the dorso-lumbar vein. 

There is also an hepatic-portal system through which blood is 
brought to the liver. The femoral veins, from the hind limbs divide, 
and their branches unite to form the abdominal vein. The abdominal 
vein also collects blood from the bladder, ventral body-wall, and heart. 
The portal vein carries blood into the liver from the stomach, intestine, 
spleen, and pancreas. 

The general circulation is brought about by the sinus venosus con- 
tracting first to force the impure venous blood into the right auricle. 
Both auricles then contract, and the oxygenated ( ) 

"blood, which was brought to the left auricle by the pulmonary veins, is 
forced into the left part of the ventricle, while the impure blood from 
the right auricle is forced into the right side of the ventricle. The 
ventricle then contracts, forcing out the impure blood. This impure 
blood first passes principally into the pulmocutaneous arteries and then 
to the lungs and skin. The oxygenated blood is pushed out later through 
the carotid and systemic arteries to the other parts of the body. The 
blood then passes through the various blood vessels which become 
smaller and smaller. These minute vessels are called capillaries. It is 
here that the food and the oxygen of the blood bathe the tissues, and 
waste-products are taken up. 

The renal-portal system carries the blood from the legs and posterior 
portions of the body to the kidneys where urea and similar impurities 
are taken out. The hepatic-portal system carries all the blood from 
the digestive tract into the liver where bile and glycogen are formed. 
All blood brought to the lungs and skin is oxygenated and carried back 
to the heart. 

The liquid in which the blood corpuscles float is called blood-plasma 
as long as it is contained within the walls of the blood vessel. When 
it leaves the blood vessel and bathes various parts of the intervening 
spaces, it is called lymph; while, if it should be taken out of the body 
entirely, it would be called serum. 

The lymph spaces in the frog's body are very large and communi- 
cate with one another as well as with the veins. There are four so-called 
lymph-hearts (Figs. 11, 347) ; two near the third vertebra, and two near 
the end of the vertebral column. These lymph-hearts force the lymph 
into the internal jugular and transverse iliac veins by their pulsation. 
The lymph itself is colorless, and whatever corpuscles it may contain are 
likewise colorless. 


As has been mentioned, breathing takes place through the skin, 
both in water and air, although the lungs are naturally the principal 
organs of respiration. The air is taken in through the external nares 
into the olfactory ( ) chamber, then through the 

The Frog 63 

internal or posterior nares into the mouth cavity. The valves then 
close; the floor of the mouth is raised, and the air is forced through 
the larynx ( ) into the lungs. The contraction of 

the body-wall forces the air back from the lungs into the mouth. It 
is interesting to note that the glottis closes, while the floor of the 
mouth alternately raises and lowers — thus drawing in and expelling air 
through the nares into the mouth cavity by what are called throat 

End of Bronchiole The lungs themselves (Fig. 15) are formed of 

minute chambers called alveoli, ( ) 

the walls of which are filled with little blood capil- 
laries. The larynx is strengthened by five cartilages, 
( ) across which the vocal 

cords are stretched. The expulsion of air from the 
Alveoli j un g S across th e f r ee ends of the vocal cords pro- 
Fig, isf Alveoli of Lungs. duces the sound known as croaking. The laryngeal 
muscles regulate the tension of the cords which causes the particular 
pitch of the sound made. 

Male frogs often have a pair of vocal sacs opening into the mouth 
cavity, serving as resonators ( ) and increasing 

the volume of the sound. 


The food taken into the body is said to be ingested. The part of 
the food which is actually taken into the blood as nutriment, is said to 
be digested, and that part of the food, which passes directly through the 
body without becoming a part of it, is said to be egested. Every living 
cell ingests and must assimilate food in order to live; consequently, it 
must also get rid of that material which has already served a nutrient 
purpose, and this getting rid of a substance, which has been digested 
and has served a purpose, is called excretion. This word must not be 
confused with secretion, which means that a substance is given off from 
the cell or gland which is to be used again by some part of the body. 

The waste matter eliminated from the body in the form of carbon 
dioxide, is thrown off through the organs of respiration, but the solid 
products have specialized organs for their removal. The skin serves as 
such an organ to a small extent. The frog does not use the skin in this 
way to the extent that human beings do, because amphibia do not 
possess sweat glands. The liver and the walls of the intestine are also 
excretory in character. 

The most important organs for excretory purposes, however, are 
the kidneys ; two oval, flattened, dark-red bodies lying behind the peri- 
toneum in the dorsal portion of the body-cavity. It is well to know that 
the kidneys are about the only abdominal organs, even in the higher 
animal forms, which lie between the dorsal peritoneum and body-wall. 
The kidneys are abundantly supplied with blood vessels, though they, 
themselves, are composed of connective tissue. The fact that so many 


General Biology 

blood vessels run to the kidneys shows that these organs are decidedly 
important. Each kidney contains a great number of coiled tubes, called 
uriniferous tubules, each one of which begins in a Malpighian body near 
the ventral surface (Fig. 16). This body consists of a knot of blood 
vessels, called the glomerulus, and a surrounding membrane, known as 
Bowman's capsule. This capsule is really the thinned out and expanded 
end of a uriniferous tubule which has become pushed in by the 
glomerulus. All excretions are carried by the uriniferous tubules to a 
collecting tubule, and thence to the ureter. The ureter of each kidney 
passes caudad ( ) toward the cloaca, emptying 

therein, thence into the bladder, a large two-lobed sac. This latter organ 

7 ffr fe vein ^ .Capillary phxus 

^lL^W??s>^7\ £olfockng iubule 




Sow man's min 
'" Capsule, 

- -Qlorn&rulus 


Fig. 16. A. Diagram Showing Formation of Renal Tubules and Bowman's Capsule. 

(After Borradaile.) 
B. Diagram Showing Relation of Glomerulus and Renal Tubules to the Blood Vessels. 

(After Guyer.) 

may be collapsed if empty ; or, if filled with the urine secreted by the 
kidney it may be considerably distended. The ventral surface of the 
kidney has a great many ciliated ( ) funnels, called 

nephrostomes (Fig. 168), whose expanded ends open into the coelom. 
In the young frog these are connected with the renal tubules, while in 
the adult they open into branches of the renal vein. The renal arteries 
and the renal-portal vein carry the blood to the kidney, leaving again 
by the renal veins. The glomeruli are supplied only with arterial blood, 
but the renal tubules receive, blood from the renal veins and to a slight 
extent from the renal arteries. 

The function of the kidney is to eliminate the waste-matter from 
the blood. The excretion itself, known as urine, is composed of a large 
number of compounds in solution. Most of the nitrogen leaves the body 
in the form of urea CO(NH 2 ) 2 , a white, crystalline compound, very 
soluble in water. 

It is interesting to note that urea was the first organic chemical 
compound actually manufactured in the laboratory. 

Urea represents the final product of the breaking down of the nitro- 

The Frog 


genous substances of the body. It has 
tion of this substance takes place to a 1 

Fig. 17. The Central Nervous System and Principal 
Nerves of a Frog, Seen From Below. 

/., Olfactory lobes; II., Optic chiasma; I.-X., cranial 
nerves; 1-10, spinal nerves; V-md.,, V.op., 
mandibular, maxillary, and opthalmic branches of 
fifth cranial nerve; VI', sixth cranial nerve after 
leaving the Gasserian ganglion; VII-hd., VII -pal., 
hyoidean and palatine branches of seventh cranial 
nerve; IX'., branch from ninth cranial nerve to seventh; 
IX"., main branch of ninth cranial nerve; X.v., tenth 
cranial nerve passing to viscera; V.x., a small twig from 
the undivided main branch of the fifth cranial nerve; X-x, 
a branch from the vagus to certain muscles; an.V., 
annulus of Vieussens through which the subclavian artery 
passes; f.t., filum terminale; G.g., Gasserian ganglion; 
hy.n., hypoglossal (first spinal) nerve; inf., infundi- 
bulum; pit., pituitary body; r.c, ramus communicans; 
sci.n., sciatic nerve; sy.c, longitudinal commissure of 
sympathetic chain; sy.g., sympathetic ganglion; v.g., 
vagus ganglion. (Redrawn from Borradaile.) 

Compare with Figures 472C, 478, 480, 483. 

been shown that the forma- 
arge extent in the liver from 
which it is given to the 
blood by a process of inter- 
nal secretion. Beside urea, 
urine contains various salts 
in solution, such as chlorides, 
sulphates, phosphates of so- 
dium, potassium, calcium, 
and magnesium, as well as 
other substances. 

So far as we know at 
this time, practically all 
excreted substances of the 
kidney pass through the 
glomeruli. The exact func- 
tion of the glomeruli is not 
known, though there are 
many theories regarding it. 
The bladder arises as an 
outpushing of the ventral 
wall of the cloaca. It is 
regarded as homologous 
( • ) with 

the allantois (Fig. 363) of 
the embryo of higher verte- 
brates. It is very distensi- 
ble. There are circular mus- 
cles at the mouth of the 
bladder which are able to 
contract and expand, the 
contraction closing the 
cloacal opening so as to 
make it possible for urine to 
collect in the bladder. 


One of the necessary 
conditions of life is what is 
commonly called irritability, 
which means that the organ- 
ism can, when properly 
stimulated, perform certain 
movements. In the higher 

66 General Biology 

forms of animals a definite nervous system does this work and permits 
a coordination of activities in different parts of the body. For example : 
In order to leap when danger threatens, the frog must be able to send 
the necessary nervous impulses to both hind legs at one time, for if 
only one leg should get an impulse, the frog would fall over on one 
side instead of propelling its body for some distance ahead. 

There is also another function performed by the nervous system. 
That is the accumulation of the effects of experiences which the animal 
in question has had, so that it may profit by the memory of these ex- 
periences in new situations. When this ability is highly developed, 
as in man, we speak of it as reasoning or intelligence. However, when 
the animal only remembers, let us say, a physical punishment for a 
given act, and by sheer association of the punishment and the act, ceases 
to perform the act which brought about the punishment, such an asso- 
ciation is not known as intelligence, but as association memory. 

Practically all parts of the body have nerves running to them. 
There are three closely associated divisions in the nervous system, 
(Fig. 17) known as : 

1. The central, consisting of brain and spinal cord. 

2. The peripheral, consisting of cerebral and spinal nerves, and 

3. The sympathetic, supplying non-striated muscles. 


As in all vertebrates, the brain and spinal cord are on the dorsal 
side of the animal, being contained within a bony case known as the 
skull and neural canal. It will be noted that beginning at the anterior 
end, the brain consists of quite distinct parts, namely, the olfactory lobes, 
the cerebral hemispheres, the two large optic lobes, a well developed 
mid brain, a small cerebellum, and a broadening of the spinal cord 
itself, called the medulla oblongata. From the ventral surface, we may 
see in addition the crossing from one side to the other of the optic nerves, 
known as the optic chiasma. 

A small process directly behind the optic chiasma, called the in- 
fundibulum, ( ) ends in another small body, 

the pituitary body, ( ) or hypophysis ( ). 

On the dorsal side of the mid brain is found the pineal gland, 
( ) or epiphysis ( ), already 

mentioned as a rudimentary organ which, in some forms of reptiles, 
forms a dorsal median eye. The cerebrum and olfactory lobes 
( ) together constitute the fore brain, the 

optic lobes form the mid brain, the cerebellum and medulla form the 
hind brain. 

It is not clear what functions each part of the frog's brain can per- 
form. From various experiments, however, it is known that the frog 
loses the power of spontaneous movement if the mid brain and cerebral 

The Frog 67 

hemispheres are removed, while the spinal cord becomes very irritable 
if the optic lobes are cut away. No function has yet been definitely 
ascribed to the cerebellum and even when all of the brain, with the 
exception of the medulla, is removed, the animal breathes normally, 
snaps at and swallows food, leaps and swims regularly, and is able to 
right itself when thrown on its back. If the posterior portion of the 
medulla is removed, the frog dies. 


The spinal cord passes down through the bony vertebral or spinal 
column. It is short and somewhat flattened. There is an enlargement 
in the brachial region where the nerves pass off to the fore limbs, and 
one further back, where the large nerves originate, which supply the hind 
legs. The cord tapers to a narrow thread, called the filum terminate, 
which extends into the urostyle. There is a median fissure on both 
dorsal and ventral sides, while from the sides of the cord the roots of 
the spinal nerves are given off. The cord itself is surrounded by two 
membranes, an outer, the dura mater, and an inner, known as the pia 
mater. There is an H-shaped central mass of gray matter consisting of 
nerve cells, and an outer mass of white matter composed of nerve fibers. 

There is a little opening through the center of the cord, called the 
central canal. The various cavities in the brain are a continuation and 
expansion of this central canal. 


The frog has ten pairs of spinal nerves, each arising by a dorsal 
and ventral root and springing from the horns of the gray matter of the 
cord (Fig. 470). The two roots unite to form a trunk, passing out be- 
tween the arches of the vertebrae. 

The brachial, or arm branches, are made up of the second, as well as 
branches from the first and third pairs of spinal nerves, and pass to the 
fore limbs and shoulder, while the sciatics arise from plexuses, composed 
of the seventh, eighth, and ninth spinal nerves, and run to the legs. 

There are also ten pairs of cranial nerves which supply the organs 
of special sense, certain muscles, various organs of the head, the heart, 
lungs, and stomach. They are named as follows i 1 

1. The olfactory ( ) nerves, running from the 

olfactory lobes to the nasal cavities. 

1 There are two additional cranial nerves in the higher animals, the spinal accessory and hypo- 
glossal, and medical students remember them by the following verse, the first letter of each word 
being the initial letter of the correspondingly numbered nerve: 

I. On 

II. Old 

III. Olympus 

IV. Towering 
V. Tops 

VI. A 













68 General Biology 

2. The optic nerves, running from the optic lobes, crossing each 
other to form the optic chiasma and passing to the eye on the opposite 
side of the head. 

3. The Oculomotor, supplying the muscles of the eye. 

4. The Trochlearis ( ), sometimes called the 
patheticus, supplying the muscles of the eye. 

5. The Trigeminus ( ), or trifacial, a sensory 
nerve, supplying the sides of the head. 

6. The Abducens ( ), supplying the muscles 
of the eye. 

7. The Facial, chiefly motor in its action and supplying the sides 
of the head. 

8. The Auditory, supplying the inner ear. 

9. The Glossopharyngeal ( ), a sensory nerve, 
supplying the pharynx and tongue. 

10. The Pneumogastric ( ), or vagus, supplying 

the larynx, heart, and stomach. 


The main trunks of this system consist of a nervous strand on each 
side of the spinal column (Fig. 337). Throughout the abdominal cavity 
one may see the chain of minute nerve ganglia, ten in number, which are 
also connected with the spinal nerves. From these chains of ganglia 
tiny nerves are given off, supplying the intestine, the kidney, and other 
abdominal organs. 

Although the sympathetic system is connected with the spinal 
nerves, it has entirely distinct and separate functions. Microscopically, 
one finds quantities of neurones, each with its little cell-body, dendrites, 
( ) and axon. These are massed in the brain and 

cord, as well as in the ganglia outside of the cord. Some of them carry 
impulses to the center and some away from it. There are several 
branches where a vast intermingling of the sympathetic strands is seen, 
the principal ones being called the coeliac, ( ) or 

solar plexus, supplying the stomach, intestine, liver, pancreas, spleen, 
and sending fibers to the gonads and kidneys, and the urogenital plexus, 
supplying kidneys and gonads primarily. 


If one marks a series of spaces on the volar ( ) 

surface of the fore arm of a human being about a millimeter square, and 

The Frog 


such person is then blindfolded, it will be found that, when a cold needle 
touches certain squares, he will feel a sensation of cold ; whereas, if it 
touches certain other squares, he will feel a sensation of heat. From 
this experiment it is learned that a great many, if not all, nerves have a 
very special and definite work to perform. 

Where a great mass of such specialized nerve endings is grouped in 
one place, it produces an organ of special sense, such as the eye, the ear, 
the nose, the tongue. All of these organs are groups of nerves whose 
endings are on the surface of some part of the body, and carry sensations 
inward to the central nervous system. These are called sensory nerves. 

The nerves which begin in the central nervous system and go out- 
ward to some of the muscles, producing various movements of those 
muscles, are called motor nerves. 

Both sensory and motor cells may unite in a ganglion and have 
both types of fibers run in the same sheath from there on ; these are 
called mixed nerves. 

m.n. p.sup.d.n.l. gl.n.l. 
• 'li 


Fig. 18. The Eye. 

A. Eye in position. d.n.L, lachrimal duct leading from eye to interior of 
nose; gl.n.l., lachrimal gland; m.n., nictitating membrane; n.a., nares; p.i., lower 
eye-lid; p. sup., upper eye-lid. (After Schimkewitsch.) 

B. Diagrammatic section through the optical axis of the eye of the frog. 

C. Diagrammatic horizontal section of the eye of man. (After Guyer.) 


Probably the most important special sense organ is the eye (Fig. 
18). Practically only one type of sensation is carried by the nerves of 
this special sense organ, and that is light perception. The eye of the 
frog is a large spherical organ similar to the eye of all of the higher 
animals. The walls of the organ are opaque with the exception of a 
transparent portion directly in the foreground, occupying about one- 
third of the eyeball, called the cornea ( ). 

The darker portion of the eye acts as does the dark chamber of a 
camera. This chamber takes up about two-thirds of the posterior part 
of the eyeball and consists of three layers. Toward the exterior is found 
the sclerotic ( ) coat made up of fibrous tissue and 

cartilage. Then follows a thin pigment-containing coat, known as the 


General Biology 

Internal ear^ 
Tympana ring 

CroS3 section 
of jaw Jluditary n&rve, „ , „ z ; / 
•f J A ^ e ^ uiia oblongata 


Posterior vertical 
Semicircular canal 

Mrrupulla - - 

Branch of 
auditory nerve 


"Eustachian iub& 

^Ant&rwr vertical 
semicircular canal 

choroid, ( ) and in the inside of this a very thin 

layer, known as the retina ( ). It is the retina which 

is sensitive to light. Almost in the center, but a little to one side of the 
back chamber, the optic nerve enters, spreading out on the retina, so 
that it has a considerable area which may be affected by light. The 
chamber of the eye itself is divided in two parts by a transparent, spheri- 
cal, crystalline lens which is 
Craniim held in position by several 

. Fourthvm.tricle' 11 <• r^\ 

\ Cartilaginous nodufo bands ot fibers. The lens is 

partly covered anteriorly by 
an opaque membrane, in 
reality a continuation of the 
choroid, growing out of the 
wall of the chamber on all 
sides. This membrane is 
known as the iris ( ), 

and covers the entire outer 
portion of the lens with the 
exception of the center. 
This central uncovered por- 
tion is called the pupil, and 
it is through this that light 
enters. There are pigment 
cells in the iris which give 
the color to the eye. 

Both of the eye-cham- 
bers are filled with a trans- 
parent liquid. That between 
the cornea and the lens is 
called the aqueous humor, 
( ) and that 

back of the lens, which is 
quite thick, is called the vit- 
reous humor ( ). 
The retina itself is quite 
complicated, being com- 
posed of thousands of end 
organs of sensory nerves, 
highly sensitive to the light 
focused upon it by the lens. 

There are six muscles attached to the eyeball by means of which it can 

be moved in practically any direction (Fig. 466). 

Raprasenis cochlea, of 
higher v&HeJoraUs "P. 


_ j Branch of 
^uuiiiory nerve. 

— Saccules 

1 sa.micircu.lar canal 


E V .-' 

Fig. 19. 

A. Diagrammatic transverse section of the head 
of the toad showing arrangement of the parts of the 
ear. (After Guyer from Jammes.) 

B. The labyrinth of the right ear of the frog, 
seen from the outer side. 

C. A diagram of the ear of the frog, col., 
Columella; f.o., fenestra ovalis; Eu., Eustachian tube; 
lab., part of the membranous labyrinth, containing 
endolymph; m., mouth; md., mandible; peril., peri- 
lymph; sk., skull; tym., tympanic membrane. (B and 
C, from Borradaile.) 

The Frog 71 


As has already been noted, there are really no external ears on 
the frog, although there is a rounded, flat membrane covering the real 
ear (Fig. 19). Directly beneath this outer membrane there is another 
tougher one which is known as the tympanic membrane ( ). 

It extends over a shallow, cone-shaped cavity, called the tympanum or 
ear-drum, and connects with the mouth through the Eustachian tube 

( )• 

The columella ( ), a slender bar of bone and 

cartilage, extends across this, being attached to the membrane at one 
end and connected with the inner ear at the other. It is by this little 
bar that vibrations of the outer membrane are carried to the inner ear. 
This inner ear is the real organ of hearing and is made up of the sensory 
end of the auditory nerve. The auditory nerve lies embedded within the 
skull itself. 

Several semi-circular canals are present which function as a bal- 
ancing organ so that the animal can keep an upright position. These 
form an "organ of the sense of equilibrium." 


Little is known regarding the effect that the sense of smell has 
in the life of a frog, but it is known that there are little olfactory sacs 
just within the bones into which the openings from the nostrils lead. 
The air enters these and then passes through the bones into the mouth 
by the internal nares. The ending of the olfactory nerve is in this little 
sac, where it is spread out to a considerable extent and where vapors 
of various kinds in the air may affect it. 


The sense of taste probably resides in the tongue, though there are 
various small structures on the roof and floor of the mouth which may 
■have similar functions. 

Conclusions of this kind are based on observations of what the frog 
does when liquids of different taste are brought in contact with the 
structures mentioned. 

The fact that the animal does react differently to different tastes 
is again accounted for by the fact that there are nerve endings in these 
probable taste organs. 


These senses are located in those portions of the skin in various 
parts of the body where many sensory nerves terminate. Just as the 
experiment of the cold needle in contact with the arm of man demon- 
strates particular sensations for particular nerve endings in man, so we 


General Biology 

Pro. /./>. /•'. 

Fig. 20. The Axial Skeleton of the Frog. 

A. The skull and vertebral column of frog viewed from dorsal surface. 

B. The same from the ventral surface. 

C. Lateral view of the urostyle; a bristle is passed through the foramen for 
the tenth spinal nerve. 

D. The branchial skeleton of the frog: O., orbital fossa; pmx., premaxilla; 
mx., maxilla; q-j., quadrato-jugal; na., nasal; pf., parieto-frontal; c, exoccipital; 
fm., foramen magnum; pro., prootic; sq., squamosal;, sphenethmoid; par., 
parasphenoid; pal., palatine; vo., vomer; ptg., pterygoid; av., atlas; c, centrum; 
ar., neural arch; zyg., zygapophysis ; trv., transverse process; ur., urostyle; H., 
body of hyoid; Ha., anterior cornu; H.p., posterior cornu of hyoid. 

E. The skull of a frog, seen from the right side: a.c, Anterior cornu of hyoid; 
a.sp., angulo-splenial; b., body of hyoid; col., columella; d., dentary; c.n., external 
nasal opening; f.p., fronto-parietal; m., maxilla; mm., mentomeckelian; n., nasal; 
o.c, occiptal condyle; p.c, posterior cornu of hyoid; p.m., premaxilla; pro., prootic; 
pt., pterygoid; q., quadrate; q.j., quadratojugal; sp., sphenethmoid; sq., squamosal. 

F. The skull of a frog seen from behind: col., Columella; ex., exoccipital; 
f.m., foramen magnum; o.c, occipital condyle; pro., prootic; pt., pterygoid; q., 
quadrate; q.j., quadratojugal; sq., squamosal; IX. X., foramen for ninth and tenth 
cranial nerves. 

G. The cartilaginous skull of a frog, seen from above after the removal of 
most of the bones: a.f., Anterior fontanelle; au., auditory capsule; cr., cranium; 
ex., exoccipital; l.p.f., left posterior fontanelle; nas., nasal capsule; o.c, occipital 
condyle; pro., prootic; pt., pterygoid; q., quadrate; q.j., quadratojugal; sp., 
sphenethmoid; u.j., upper jaw bar. 

The Frog 73 

suppose that different end-organs in the skin of the frog may also have 
definite functions. 


The frog is possessed of an endoskeleton as is man. The bones and 
cartilages constituting this endoskeleton furnish a support which holds 
the muscles and organs of the body in position. 

For convenience sake the skeleton is divided into two parts, the 
axial portion (Fig. 20), comprising skull and vertebral column, and the 
appendicular portion (Figs. 21, 22), consisting of the pectoral or shoul- 
der, and pelvic or hip girdles, together with the bones of the limbs which 
these girdles support. 

The frog's skeleton consists of about ninety articulated bones 
(united at the joints). The skull has the various bones comprising it 
so firmly fused that they appear as a single bone. Even the seemingly 
single bone of the fore arm will be found to consist of two bones which 
have fused together. 


This is divided into the skull [cranium ( ) and 

visceral skeleton ( ) ] , and the vertebral column. The 

two divisions of the skull just mentioned are made up of the brain case 
together with the auditory ( ) and olfactory cap- 

sules ( ). These constitute the cranium. The jaws 

and hyoid arch ( ) together, form the visceral 


The inside of the cranium, where the brain is placed, is known as 
the cranial cavity. The skull itself is composed of thirty-two bones and 
cartilages fused together so as to appear almost a solid structure. The 
cranial bones form the roof, walls, and floor of the cranial cavity. 

The floor is composed of the basioccipital ( ) 

and the parasphenoid ( ). 

The walls consist of the parietals ( ), the otic 

bones ( ), and the exoccipital ( ). 

The roof is made up of the supraoccipital ( ) 

and the frontals. 

The facial bones, forming the face, consist of nasals ( ), 

the premaxillas ( ), and the maxillas ( ) 

above, and vomers ( ) below. The premaxillas and 

the maxillas, however, are a part of the visceral skeleton, comprising, 
together with a pair of quadrangulars, the upper jaws. 

H and I. Vertebrae of a frog. H, fourth vertebra, seen from in front; I, sixth 
and seventh vertebrae from the right, as., Prezygapophysis; cen., centrum; n.a., 
neural arch; n.c, vertebral foramen; n.s., neural spine; pz., postzygapophysis; r.c, 
cartilage at end of transverse process; tr., transverse process. 

(A, B, C and D from Bourne, after Ecker. E, F, G, H and I, after Borradaile.) 

74 General Biology 

The maxilla and the premaxilla bear teeth. The lower jaw, or 
mandibular arch ( ), is made up of a pair of carti- 

laginous rods (Meckel's cartilages), enforced by a pair of dentary bones 
( ) and a pair of angulo-splenials ( ). 

The jaws themselves are attached to the cranium by an apparatus con- 
sisting of squamosals ( ), pterygoids ( ) 
and palatines ( ), the whole often known as a sus- 
pensory apparatus, or a suspensorium ( ). These 
bones, though attached to the cranuim in the adult frog, are at first free 
from it, being in reality the upper parts of what are called visceral 
arches, which lie below the cranium. The second arch is called the 
hyoid, and is quite rudimentary, only a small part of it being left in the 
adult frog. In the higher animal forms, such as man, this is a well- 
developed V-shaped arch to which the tongue is attached ; but in the frog 
it remains only as a flat plate, partly bone and partly cartilage, so loosely 
attached to the skull that it is quite easily, and one might add, usually, 
lost. It lies directly beneath the larynx ( ) in the 
frog, giving this support and rigidity, being connected with the skull by 
ligaments ( ) only. 

In the young frog all parts of the skull are soft, but true bone forms 
as development goes on. A part of the skull forms originally as 
cartilage, a material that is harder than membrane but softer than bone. 
Mineral matter is deposited a little later in the cartilage, causing ossifi- 
cation ( ) or true manufacture of bone. 

Bones, such as the occipitals, parietals, pterygoids, and the mandi- 
bles, formed from cartilage, are known as cartilaginous bones, the other 
ones being manufactured first as membranes. Here, too, mineral matter 
is laid down and the structures become hardened. Such bones as 
frontals, parietals, parasphenoids, squamosals, nasals, vomers, pre- 
maxillas, and maxilla, are of the latter kind and are called membrane 
bones. The projections at the posterior end of the skull, where it 
connects with the vertebral column, are called occipital condyles 
( ) ; and the large opening directly between these, 

through which the spinal cord continues down through the bony canal 
of the spinal column, is called the foramen magnum ( ). 


This consists of nine separate segments of bone (H and I, Fig. 20), 
each known as a vertebra ( ), and a long platelike 

posterior extension, the urostyle ( ). Each vertebra, 

consists of a centrum and a neural arch ( ), the 

latter enclosing the neural foramen. On each side of all but the first 
vertebra there is found a transverse process, while all vertebrae possess 
a dorsal spine and a pair of smooth surfaces where each successive verte- 
bra rests upon the next following. These articulating processes are 

The Frog 


called .zygapophyses ( ). The little bones themselves 

are held together by ligaments and move on one another by means of the 
centrum and zygapophyses. This permits a firm axial support, while 
also allowing for the bending of the body. By having all the vertebrae, 
one immediately above the other, the neural opening is continuous, so 
that the spinal cord not only lies free, but the vertebrae themselves are 
thus prevented from bending sufficiently to damage the cord. 

The surfaces of the centra unite by a ball-and-socket joint. Each of 

the first seven vertebrae possesses a 
ball on the posterior and a socket 
on the anterior surface. The eighth, 
however, is concave on both sur- 
faces and the ninth is convex on 
both. It is important to know the 
difference in action which this en- 
tails. Although all nine vertebrae 
are much alike, they can easily be 
distinguished from one another. The 
first possesses no transverse process, 
while the centrum of the ninth has 
two convex posterior surfaces and 
very large transverse processes. It 
is from this last vertebra that the 
urostyle, the long slender bone, ex- 
tends backward to the end of the 

The urostyle is supposed to rep- 
resent the tail found in allied ani- 
mals, such as the salamanders. The 
spinal cord actually extends into 
the urostyle, but passes out almost 
immediately through two small 
openings on either side, as two 
rather tiny filaments. 

There are no ribs in the frog, 
and the transverse processes end 
rather abruptly a very short distance from the centrum. 

Fig. 21. 
Pectoral Girdle, Arm, and Hand, of Frog. 

A. The shoulder girdle of the frog; the 
scapula and suprascapula are turned outwards. 
ep., episternum; os, omosternum; ep.c, 
epicoracoids; mes., mesosternum; xi., xiphister- 
num;, suprascapula; sc, scapula; gl., 
glenoid cavity; cor., coracoid; cl., clavicle. 

B. Forearm and hand of right side, as seen 
from above; ru., radio-ulna; / — V., the five 
digits; r., radiale; im., intermedium; u., ulnare; 
a., first distal carpal bone; b., second distal; 
c, third distal. 

C. Radio-ulna of right side: o., olecranon; 
r., radius; u., ulna. 

D. Humerus: h., head; sh., shaft; ar., dis- 
tal articular knob; t., trochlea. (From Bourne, 
after Ecker.) 


The shoulder, or pectoral girdle, ( ) (Fig. 21) 

serves as an attachment for the muscles which move the fore limbs, and 
also as a protection for the organs in the anterior portion of the trunk. 

The girdle itself surrounds the body just back of the head, consist- 
ing of a paired scapula ( ), the dorsal part of which 


General Biology 

is made of cartilage, a coracoid ( ), a precoracoid 

or epicoracoid, and a clavicle ( ) fused together. 

At the meeting of coracoid and scapula there is a little smooth cavity 
where the arm joins the girdle called the glenoid fossa ( ). 

Where coracoid and clavicle meet at the mid line on the ventral side 
of the body, there are four bones. These four actually are a part of the 
axial skeleton, but are usually classified as a part of the appendicular 
as well. The most anterior one of the bones is called the episternum, 
the one between this and the clavicle is the omosternum, while the pos- 
terior one closest to the omosternum is the mesosternum, and the one 
projecting farthest backward is the xiphisternum. 

The fore limbs are made up of a long bone, the humerus 
), joining the pectoral girdle in the glenoid fossa 
) and with the radio-ulna at 
). This latter bone constitutes the 
skeleton of the fore arm and in reality consists of two bones, the radius 
and the ulna, fused together. 


at its proximal end ( 
the distal end ( 

B '«* 

Fig. 22. The Pelvic Girdle and Leg. 

A. Pelvic girdle complete. 

B. One side of pelvic girdle: II., ilium; Isch., ischium; Pu., cartilaginous 
pubis; Ac, acetabulum. 

C. Femur of the frog: p., proximal; d., distal articulating surfaces; s., shaft. 

D. Tibio-fibula, seen from below: p., proximal; d., distal articulating sur- 
faces; t., tibial half of the bone separated by a groove from /., the fibular half. 

E. The right ankle and foot of the frog, seen from below: This figure is 
drawn to a larger scale than A and B. a., astragalus; c, calcaneum; / — V., the 
five principal digits; X., the minute accessory digit. (From Bourne after Ecker.) 

The wrist possesses six bones, the ulnare ( ), 

radiale, ( ), intermedium, and three carpals 

( )• 

The hand has five proximal metacarpal ( ) 

bones, followed in digits ( ) II and III by two 

phalanges ( ), and in digits IV and V by three 


The pollex, ( ) or thumb, is rudimentary. 

The Frog 77 

The pelvic, ( ) or hip girdle, (Fig. 22) supports 

the hind limbs, and consists of two sets of three parts each, the ischium 
( ), ilium ( ), and the pubis 

( ), the latter being cartilaginous, strongly united. 

The edge of the hip girdle is called the crest. The meeting of the two 
pubic bones forms a symphysis ( ). The anterior 

end of each bone is attached to one of the transverse processes of the 
arched vertebra. The little cup-shaped opening, where the three bones 
just mentioned meet, is called the acetabulum ( ). 

It is in this concavity that the head of the femur ( ), 

the long bone in the thigh, lies. 

The hind limb consists of a thigh ( ) with the 

femur as its solitary bone. The leg proper, running from knee to ankle, 
is made up of the tibia ( ) and fibula ( ) 

fused together, called the tibio-fibula, or leg bone. 

Note the ridges on these long bones for the attachment of muscles. 

There are four tarsal bones ( ), the astragalus 

( ), the calcaneum ( ), and two 

smaller ones. 

The foot has five complete digits as well as an extra or super- 
numerary toe. Each digit has one proximal metatarsal bone, while 
beyond these there are a variable number of phalanges. The hallux 
( ), corresponding to the great toe of man, is the 

smallest of the series. It has one metatarsal and two phalanges. On 
the inner side of the hallux is the calcar ( ), an extra 

toe. It may have one or two joints and a short metatarsal. 


All movements in the body are produced through the contraction 
of some one or more muscles. The muscles in turn are innervated 
( ) by one or more nerves. The muscle is usually 

attached by one or both ends to a bone, so that a good leverage is 
obtained. In some cases the attachment is direct. In others the muscle 
is attached by means of a tendon. A tendon is a band of tough, some- 
what inelastic, connective tissue which is in reality the continuation of 
the muscle fascia after the muscle itself ends. 

Contraction may be brought about by many causes, such as heat, 
pressure, electrical, or chemical stimuli ( ). 

There are three distinct types of muscles (Fig. 23) ; each type has 
a more or less individual, cellular arrangement. These three types are 
known as heart muscle, voluntary or striated muscle, and involuntary 
or nonstriated muscle. 

Striated muscle can be moved when the individual possessing it so 
desires. Such are the muscles of the arm and hand. Examples of non- 
striated muscle may be found in the blood vessels, where the desire of 
the individual has little or nothing to do with the contraction and 


General Biology 

expansion of circular and longitudinal muscles contained within the walls 
of the blood vessels themselves. 

The outer surface of all muscles is covered by a connective tissue 
membrane called fascia ( ), which is not very elastic. 

The fascia usually becomes thicker toward the end of the muscle, gradu- 
ating in a dense, fibrous band called a tendon or, if this tendon is broad 
and flat, an aponeurosis ( ). 

That part of the muscle most thoroughly attached — usually to a 
relatively immovable part and most frequently toward the center of the 
body — is called its origin. The more movable and distal attachment is 
known as its insertion. 

The action of a muscle in con- 
tracting is to draw origin and inser- 
tion closer together. 

Whenever a muscle moves any 
part of the body in its normal direc- 
tion or as one may say, with the 
joint, such movement is called 
flexion ( ) ; against 

the joint, extension ( ). 

A muscle which pulls any limb or 
portion of a limb away from the 
central axis of the body is an ab- 
ductor ( ), and 
one which draws the limbs or their 
appendages toward the center of the 
body is an adductor ( ). 
Rotators ( ) are 
those which cause the limb to rotate 
about its axis, such as those turning 
the femur at the hip ; levators raise 
a part, such as the lower jaw; and 
depressors produce the opposite 

To know a muscle there are five 
points which must be remembered: 

(1) Its Origin. 

(2) Its Insertion. 

(3) Its Relation to other struc- 

(4) Its Innervation. 

(5) Its Action. 

Fig. 23. Different Types of Muscle-Fibres. 

A., embryonic striped muscle-fibre_ from the 
tail of a tadpole, showing the nuclei nn., and 
the protoplasm p., of the ccenocyte from which 
the fibres are developed. The fibres exhibit 
alternate dark and light bands, and in the 
center of each dark band is a light line, the 
line of Hensen. 

B., cardiac muscle-fibre showing the short 
branched nucleated cells. 

C, a single cell from cardiac muscle-fibre 
more highly magnified, showing the cross- 
striation and the nucleus n. 

D., group of unstriped muscle-fibres from 
the bladder: a., the nuclei; p., the granular 
remains of the cell protoplasm; /., the longi- 
tudinally striated contractile portion. (A and 
D, from Bourne. B and C from Schafer.) 


The following list will convey a clear and accurate idea of what 
is essential in the study of the muscular system (Fig. 24). The rela- 

The Frog 79 

tions of each muscle to surrounding structures can be obtained only 
by a dissection of the animal and a thorough study of the drawings. 


1. Muscles of the lower or ventral side. 

(a) Muscles of the abdomen. 

e. g. Rectus abdominis, a wide band running along the abdo- 
men, divided lengthwise down the middle by the connective tissue linea 
alba and transversely by tendinous intersections. Its origin is at the 
pubic sympysis and its insertion at the sternum. 

Obliquus externus, a broad sheet at each side of the body, 
arising from an aponeurosis known as the dorsal fascia which covers 
the muscles of the back, and inserted into the linea alba above the rectus 

Obliquus interims and transversus, muscular sheets below the 
external oblique. 

By their contraction, all these muscles lessen the size of the body 
cavity and compress the organs within it. 

Innervation : All of these muscles are innervated by twigs from 
IV, V, VI and VII spinal nerves. 

(b) Muscles of the Breast Region. 

e. g. Pectoralis, large and fan-shaped, inserted into the deltoid 
ridge of the humerus and consisting of a sternal portion which arises 
from the pectoral girdle, and an abdominal portion which arises from 
the aponeurosis at the side of the rectus* abdominis. 

It draws down the arm. 

Innervation : Twig from II spinal nerve. 

Coraco-radialis, arising from the coracoid and inserted into the 
upper end of the radius. It bends the arm. 

Innervation : Twig from II spinal nerve. 

2. Muscles of the Back. 

(a) Muscle inserted into the lower jaw. 

Depressor mandibulae, triangular, arising from the supra- 
scapula and inserted into the angle of the lower jaw, which it draws 
downwards and backwards, thus opening the mouth. 

(b) Muscles inserted on the fore-limb. 

e. g. Latissimus dorsi ( ) triangular, 

arising from the dorsal fascia and inserted into the deltoid ridge. It 
draws back the arm. 

Infraspinatus, in front of and similar to the latissimus dorsi. It 
raises the arm. 


General Biology 

Innervation : Twig from II spinal nerve. 

(c) Muscles inserted into the shoulder girdle. 

e. g. Levatur anguli scapulae, arising from the skull and in- 
serted into the under side of the suprascapula, which it draws forward. 
Innervation : Twig from I spinal nerve. 

Fig. 24. A — A Ventral View of the Muscular System of a Frog. 

ad. long., Adductor longus; ad.mag., adductor magnus; anc, anconaeus; cor.rad., 
coraco-radialis; dtd., deltoid; e.ob., external oblique;, extensor cruris ;gast., 
gastrocnemius; grac, gracilis; I. a., linea alba; pct.ab., abdominal part of the pectoral 
muscle; pot. St., sternal part of the same; r.ab., rectus abdominis; sar., sartorius; 
sm., mylohyoid; t.i., tendinous intersections; t.A., tendo Achillis t.f., tibiofibula; 
tib-ant., tibialis anterior;, tibialis posterior; v. int., vastus internus; x.c, 
xiphoid cartilage. (After Borradaile.) 

B. Dissection of special muscles of the left hind leg of the toad (redrawn from 
Jammes). Muscles shaded in black are extensors, in gray, flexors. 

The Frog 81 

Serratus, arising from the little knobs on the transverse 
processes of the vertebrae which represent the ribs, and inserted into the 
under side of the suprascapula, which it draws backwards, outwards, or 
inwards, according to the division which is contracted. 

(d) Muscles inserted into the hind-limb. 

e. g. Gluteus (iliacus externus, or gluteus medius), arising 
from the ilium and inserted into the head of the femur, which it rotates 

(e) Muscles inserted into' the hip girdle. 

e. g. Coccygeo-iliacus, arising from the urostyle and inserted 
into the ilium, which it holds firm as a fulcrum for the movements of the 

(f) Muscles of the Backbone. 

e. g. Longissimus dorsi, a band running the whole length of 
the back, divided by tendinous intersections, which are attached to the 
transverse processes, and inserted in front into the skull. It straightens 
the back. 

Innervation : Twig from I spinal nerve. 


1. Muscles underneath the Head. 

e. g. Sternohyoid, from hyoid to pectoral girdle. 

Geniohyoid, from hyoid to chin. 

Hyoglossus, from hyoid to tongue. 

Petrohyoid, from hyoid to auditory capsule. 

Mylohyoid, submandibular, or submaxillaris ( ), 

a sheet of muscle running from side to side of the lower jaw. These 
muscles alter the position of the floor of the mouth. 

Innervation : Twigs from I spinal nerve. 

2. Muscles of the Lower Jaw. 

e. g. Temporalis and masseter ( ), arising 

from the skull and inserted into the lower jaw, which they raise. 
Innervation : Mandibular branch of the V cranial nerve. 

3. Muscles of the Eyeball (Fig. 466). 

Rectus superior, r. inferior, r. externus, r. internus, arising from 
the skull in the hind part of the orbit and inserted into the eyeball. 

Innervation: All but the rectus externus from the III cranial 
nerve. The r. externus by the VI cranial nerve. 

Obliquus superior and o. inferior, arising from the skull in the 
front part of the orbit and inserted into the eyeball. 


82 General Biology 

Innervation : Obliquus superior by the IV cranial nerve and o. 
inferior by the III cranial nerve. 


1. Muscles of the Upper Arm. 

e. g. Deltoideus, arising from the scapula and inserted into the 
humerus. It raises the arm. 

2. Muscles of the Fore-Arm. 

Triceps brachii or anconaeus ( ), arising 

from the scapula and humerus, and inserted into the upper end of the 
ulna. It straightens the arm. 

There is no Biceps muscle in the arm of the frog. 

3. The muscles of the Wrist and Fingers are numerous and com- 

Innervation : Branches and twigs of II spinal or brachial 
nerves innervate all arm and finger muscles. 


(1) Superficial muscles of the Thigh on the Preaxial (apparent 
ventral 1 Surface. 

1. Sartorius ( ), a long, narrow band arising 
from the lower end of the ilium, lying obliquely upon the abductor 
magnus, and inserted into the tibia on its inner side near the end. It 
bends the knee. 

2. Adductor magnus, a large muscle arising from the pubis and 
ischium, lying along the inner border of the sartorius and inserted 
into the femur near its lower end. It draws the thigh toward the body. 

3. Adductor longus, a long, narrow muscle lying along the outer 
side of the adductor magnus, and often completely hidden by the 
sartorius ; it arises from the iliac symphysis beneath the sartorius, and 
unites a little way beyond the middle of the thigh with the adductor 
magnus. It adducts the thigh and draws it ventrally. 

4. Gracilis major ( ), or rectus interims major, 
is a large muscle arising from the ischium, lying along the inner side of 
the adductor magnus, and inserted into the inner-side of the head of the 
tibia. It bends the knee. 

5. Gracilis minor, or rectus internus minor, is a narrow flat band of 
muscle running along the inner, or flexor margin of the thigh. It rises 
from a tendinous expansion connected with the ischial symphysis, and 

^he femur of the frog rotates away from the midline more than does the femur of man. 
Consequently the true outer border of the frog's thigh is equivalent to the inner border of man's. 
In other words the preaxial surface of the frog's thigh is equivalent to the inner surface of man's. 

The Frog 83 

is inserted into the inner side of the tibia, just below its head. Its action 
is the same as for gracilis major. 

Innervation: Branches and twigs from the sciatic nerve and 

(2) Superficial muscles of the Extensor Surface of the Thigh. 

1. Triceps extensor femoris, or cruris, a very large muscle 
inserted into the front of the tibia just below the head of the latter, but 
arising from the pelvic girdle as three separate muscles, the rectus ami- 
cus femoris ( ), vastus externus ( ), 
and vastus internus, or crureus ( ). All these lie 
on the front of the thigh, and their action is to straighten the knee. 

Innervation : Branches and twigs from the sciatic nerve and 

(3) Superficial muscles of the Postaxial Surface (apparent dorsal) 
of the Thigh. 

1. The gluteus (iliacus externus), already mentioned, lies in 
the thigh between the rectus anticus femoris and the vastus externus. 
It draws the thigh forward. 

2. The biceps (ileo-fibularis) is a long slender muscle which 
arises from the crest of the ilium just above the acetabulum. It lies in 
the thigh along the inner border of the vastus externus, and is inserted 
by a flattened tendinous expansion into the distal end of the femur and 
the head of the tibia-fibula. It draws the thigh dorsally and flexes the 

3. The semimembranosus is a stout muscle lying along the 
inner side of the biceps, between it and the rectus internus minor. It 
arises from the dorsal angle of the ischial symphysis just beneath the 
cloacal opening, and is inserted into the back of the head of the tibia. 
It is divided about its middle by an oblique tendinous intersection. It 
adducts the thigh and flexes or extends the leg according to whether 
the leg is in a flexed or extended position, 

4. The pyriformis is a slender muscle which arises from the 
tip of the urostyle, passes backward and outward between the biceps 
and the semimembranosus, and is inserted into the femur at the junction 
of its proximal and middle thirds. It pulls the urostyle to one side and 
draws the femur dorsally. 

Innervation : Branches and twigs from sciatic nerve and 

(4) Deep muscles of the Thigh. 

1. The semitendinosus is a long thin muscle which arises by 
two heads ; an anterior one from the ischium close to the ventral angle 
of the ischial symphysis and the acetabulum ; and a posterior one from 

84 General Biology 

the ischial symphysis. The anterior head passes through a slit in the 
adductor magnus and unites with the posterior head in the distal third 
of the thigh. The tendon of insertion is long and thin, and joins that 
of the rectus internus minor to be inserted into the tibia just below its 
head. It adducts the thigh and flexes the leg. 

2. The adductor brevis is a short, wide muscle, lying beneath 
the upper end of the adductor magnus. It arises from the pubic and 
ischial symphyses, and is inserted into the preaxial surface of the proxi- 
mal half of the femur. 

3. The pectineus ( ) is a rather small 
muscle, lying along the outer (extensor) side of the adductor brevis. 
It arises from the anterior half of the pubic symphysis in front of the 
adductor brevis, and is inserted like it into the proximal half of the 

4. The ilio-psoas (iliacus internus) arises by a wide origin 
from the inner surface of the acetabular portion of the ilium. It turns 
round the anterior border of the ilium, and crosses in front of the hip- 
joint, where, for a short part of its course, it is superficial between the 
heads of the vastus internus and of the rectus anticus femoris. It then 
passes down the thigh beneath these muscles, and is inserted into the 
back of the proximal half of the femur. It draws the thigh forward. 

5. The quadratus femoris is a small muscle on the back of the 
upper part of the thigh ; it arises from the ilium above the acetabulum, 
and from the base of the iliac crest; it lies beneath the pyriformis and 
behind the biceps, and is inserted into the inner surface of the proximal 
third of the femur between the pyriformis and the ilio-psoas. 

6. The obturator is a deeply situated muscle which arises from 
the whole length of the ischial symphysis and the adjacent parts of the 
iliac and pubic symphyses, and is inserted into the head of the femur 
close to the gluteus. 

Innervation: Branches and twigs from sciatic nerve and 

5. Muscles of the Leg or Shank. 

e. g. (1) Peroneus, a long muscle which arises from the end 
of the femur, lies along the side of the tibio-fibula, and is inserted into 
the end of the tibia and the calcaneum ( ). It 

extends the leg and the foot and flexes the foot. 

Innervation : Peroneus nerve. 

(2) Gastrocnemius ( ), a large, spindle- 

shaped muscle which forms the "calf." It arises from the hind side of 
the end of the femur and tapers into the long tendo Achillis, which passes 
under the ankle joint and ends in the sole of the foot. It straightens the 
foot on the shank. 

Innervation : Tibialis nerve. 

The Frog 85 

(3) Tibialis anticus, arising from the front of the femur by a 
long tendon, lies in front of the shank and divides into two bellies, 
which are respectively inserted into the astragalus and calcaneus. It 
bends the foot on the shank. 

Innervation : Peroneus nerve. 

(4) Tibialis posticus arises from the whole length of the flexor 
surface of the tibia. It ends in a tendon which passes round the inner 
malleolus ( ), lies in a groove in the lower end of 
the tibia and is inserted into the dorsal surface of the astragalus. It 
extends the foot when flexed, and flexes the foot when extended. 

Innervation : Tibialis nerve. 

(5) Extensor cruris lies along the preaxial side of the tibialis 
anticus partly covered by this and partly by the strong fascia of the 
leg. It arises by a long tendon from the preaxial condyle of the femur, 
runs in a groove in the upper end of the tibia, and is inserted into the 
extensor surface of the tibia along nearly its whole length. It extends 
the foot. 

Innervation : Tibialis nerve. 

6. Muscles of the Foot. 

These, just as the muscles of the wrist and hand are many and 
complicated, but the student should know at least the general location of 
the following: 

Aponeurosis plantaris. 

The flattened and broadened continuation of the tendon of the 
gastrocnemius muscle passing over the heel and spreading out on the 
sole of the foot in a sort of triangle with the base toward the toes. 
Where the aponeurosis crosses the heel it is. known as the tendon of 

Flexor digitorum I, II, III, IV, V. 

Each digit usually has a flexor, extensor, abductor, and ad- 
ductor bearing the number of the toe to which it is attached, the great 
toe being I. 

There are also small interosseus muscles between the various 
tarsal bones. 

For a detailed account of all muscles of the frog see : Ecker's 
"The Anatomy of the Frog." (Oxford University Press.) 


The sexes are separate in the frog. The male has a rather thick pad 
on the underside of its thumb, larger in the spring, at the breeding sea- 
son, than at any other time of the year. The two rounded or oval 
spermaries (A, Fig. 25), of a light yellow color, are found at the upper 


General Biology 

end of the kidneys, while branching masses of a yellow shade are usually 
attached to them. The sperm, the male gamete ( ), 

is produced in the spermaries, being carried through slender ducts, the 
vasa efferentia, through the kidney to empty into the ureters. It will 
be observed, therefore, that in the male frog the ureters serve both as 
an exit for the excretion of the kidneys and for the secretions of the 
spermaries. In some species of frogs, the ureters are slightly enlarged 
to form a small sac just where they enter the cloaca. Such sacs are 

aoJ>. coel.mes. 


Fig. 25. The Urogenital Organs of the Frog. A, Male; B, Female. 

ao.b., systemic arteries; ao.c, main aortic trunk; cav.i., vena cava inferior; 
cl., cloaca (dissected from the ventral side); coel,mes., coeliaco mesenteric artery; 
d., large intestine; f.k., fat bodies; h.s.l., urogenital duct; h.s.l.', entrance of uro- 
genital duct into cloaca; il., iliac artery; n., kidney; neb.n., adrenal bodies; ost.abd., 
funnel-shaped opening of oviduct; ov., ovary; ovid., oviduct; ovidJ ', entrance of 
oviduct into cloaca; test., testes; ut., uterus; ves., urinary bladder; ves.', opening 
of bladder into cloaca; ves.sem., seminal vesicle; w., Wolrian duct; w.' , opening of 
Wolfian ducts. (After W. Meissner.) 

known as seminal vesicles. The sperm are held there until ready to be 

If the body of a female (B, Fig. 25) be opened in the breeding season 
the ovaries will be found filled with eggs which seem to fill almost the 
entire body-cavity. The ovaries, the female gonads ( ), 

are placed in a position corresponding to the spermaries in the male. If 
it is not the breeding season, the ovaries are rather small, slightly folded 
and leaf-life, not very much larger than the spermaries, but of a differ- 
ent shape. The eggs break out of the ovary into the body-cavity and 

The Frog 87 

make their way into the coiled oviduct through a small opening, passing 
down into the thin- walled distensible uterus ( ). 

The oviducts themselves are not directly connected with the ovaries, 
but lie coiled next to the kidneys, the anterior end being a funnel-shaped 
opening. The tube itself passes caudad beside the kidney to open 
into the cloaca. The uterus is the rather large thin-walled chamber at 
its termination, in which the eggs are stored after passing through the 
oviducts until the final ^gg laying. The oviducts themselves, like the 
ovaries, vary in size at different seasons of the year. 

The gelatinous substance covering the eggs is secreted by little 
glands in the oviducts, called nidamental glands (Lat. nidus=a nest). 
It is to be observed that the sexual organs and kidneys lie close together 
and have a common opening, and in the male the same duct, namely, 
the ureter, serves for an exit of both sperm and urine. A similar close 
relation is found in nearly all other vertebrates, and when the study of 
embryology is taken up it will be found that the ducts and kidneys were 
originally derived from the same. region of the embryo. It is, therefore, 
common to speak of the excretory and reproductive system together as 
the urogenital system. 


Directly in front of the gonads, we find a yellow organ with many 
finger-like processes known as a fat body. It has a broader and closer 
attachment to the anterior end of the male gonad than it has to the 
female ovary. It is supposed to serve as a storehouse of nutriment, for 
it varies in size and shape at different seasons of the year. Nearly all 
the fat disappears from the cells in spring while as soon as the feeding 
period begins the fat increases. 

References : 

Ecker, "The Anatomy of the Frog." 
Holmes, "The Frog." 

Parker & Haswell, "Textbook of Zoology." 
Bourne, "Comparative Anatomy of Animals." 
Borradaile, "Manual of Zoology." 
Schaefer, "The Endocrine Organs." 
Bandler, "The Endocrines." 



IT will be observed later in the study of the histology of the frog 
that the different types of cells vary in size and shape. Some are 
round, others more or less cuboidal, still others cylindrical, etc. As 
there are animals possessed of but a single cell which can nevertheless 
perform all acts necessary to a complete organism and, consequently, 
can lead an independent existence, the cell is called the biological unit, 
and facts in the biological world are not considered explained until they 
have been reduced to terms of cell units. 

Not a living thing, plant or animal comes into existence which does 
not start life as a single cell. It is, therefore, an axiom ( ) 

of science that there can be no living cell unless it sprang from a previous 
cell. Therefore, an egg, regardless of whether it be the small egg of a 
frog or so large a one as that of the ostrich, is only a single cell. In 
fact, in the hen's egg usually used in the laboratory for experimentation, 
the yolk represents the food for the offspring, the egg proper being that 
little portion, about the size of a dime, which always floats on the top 
of the yolk, regardless of the position of the egg. 

The following drawing (Fig. 26) is that of an ideal cell. This means 
that everything which the student will ever find in any cell, plant or 
animal, is contained in this drawing. One must remember, however, 
that search may be made from now until the end of time and no one cell 
may ever be found with all the parts shown in this ideal cell. 

Lmin ^Vof-tUO-k — 


u *r h 

Fig. 26. An Ideal Cell, 

The Cell 89 

The entire substance surrounded by the cell wall is called proto- 
plasm. This is a jelly-like, or viscous, material something like the white 
of an egg. Probably most cells have a definite wall, though many animal 
cells do not. On the inside of this cell wall there is a network, or 
reticulum, in which are found little foreign bodies, plastids, and open 
spaces called vacuoles. The network itself is called spongioplasm, be- 
cause it somewhat resembles a sponge. The liquid protoplasm on the 
inside of this network is called hyaloplasm ( ). On 

the inside of the cell there is a seemingly smaller cell, called the nucleus. 
This nucleus is considered the most important part of the cell. A cell 
may have one nucleus, or it may have many. There is a nuclear wall 
just as there is a cell wall, and on the inside of the nucleus there is also 
a network or reticulum. 

When a cell has been chemically stained with various substances, 
it is found that a portion of the network in the nucleus takes the stain, 
while a portion does not, showing that this nuclear network is composed 
of at least two different substances. The part which takes the stain is 
called the chromatin ( ) network, and the part 

which does not take the stain is called the linin ( ) 

network. This nuclear network which takes the stain usually stands 
out quite distinctly from the rest of the cell, making it appear at first 
glance as though the entire nucleus had taken a great quantity of stain 
to itself. 

The substance lying within the network of the nucleus is called 
nucleoplasm. It may happen that some cells do not have a definitely 
outlined nucleus with a nuclear wall, but nevertheless these cells have 
nuclear material scattered throughout the cell itself in the form of 
granules; such granules are known as distributed nuclei. In the red 
blood corpuscles of the human being there are no nuclei in the adult 
form, although such red cells are nucleated when they originally begin 

On the inside of the nucleus there is in turn a smaller nucleus which 
is called the nucleolus ( ). 

At certain places in the nucleus where the various fibers of network 
cross each other, there may be little knots, called net-knots, but these 
must not be confused with the nucleoli. The chromatin itself ap- 
pears in a granular form, and the granules are called chromomeres 

( )• 

There may even be two nucleoli in one nucleus. These stain quite 
readily also, but appear somewhat different from the chromatin after 
such staining. Exactly what the nucleolus does, biologists do not know. 
It disappears during the time the cell divides and consequently has been 
thought to serve the purpose of holding something in reserve for the 
division process. 

All of the material within the cell walls, but outside the nucleus, is 

90 General Biology 

known as cytoplasm, to distinguish it from the nuclear material within 
the nuclear wall or membrane. 

Just outside of the nucleus and within the cytoplasm, there is usually 
found a tiny circle with a dot in the center. The dot itself is called the 
centrosome ( ) and the circle about it the attraction 

sphere, or centrosphere. 

There are little perforations through the nuclear wall so that there 
is a direct connection between nucleoplasm and cytoplasm. 


Bodies of a solid nature, not protoplasmic, are common to many 
cells. These are pigments, oil, fat, crystals, glycogen, starch, chlorophyl, 
etc., and are commonly spoken of as cell inclusions, though as a matter 
of fact only foreign substances such as bacteria, etc., should be called 
inclusions. Starch and chlorophyl are found almost exclusively in plant 
cells. By these inclusions the shape of the cell is often changed, and 
particularly the position of the nucleus. Fat gathers at one end of the 
cell, crowding the nucleus to the opposite extremity and displaces the 
cytoplasm to the periphery, mostly to that end of the cell occupied by 
the nucleus. Pigment may be in solution, more frequently in granules, 
and it is always found in the cytoplasm, not in the nucleus. Vacuoles 
are very common to most cells. These vary in number and size and are 
usually spherical cavities filled with fluid secreted by the protoplasm. 
The vacuoles contract, often with considerable regularity, and, as a rule, 
empty to the surface of the cell. Waste products are in this way elimi- 
nated from the body of the cell. 

The constituents of a typical cell may then be summarized as 
follows : 

1. Cytoplasm, the protoplasm that surrounds the nucleus, consist- 
ing of : 

(a) Spongioplasm, a reticulum or fibrillar network; 

(b) Hyaloplasm, a fluid portion, also called cytolymph ; 

(c) Cell membrane, often absent in animal cells. 1 

2. Nucleoplasm or karyoplasm, the protoplasm of the nucleus : 

(a) Nuclear membrane, frequently absent; 

(b) Chromatin, network that stains easily; 

(c) Linin, closely allied to the chromatin but does not stain; 

dissolves in distilled water; 

(d) Nuclear sap, a fluid perhaps analogous to the hyaloplasm ; 

(e) Nucleolus, spherical body that stains heavily; 

( f ) Nuclear net knots, or karyosomes, false nuclei that are nodal 
points formed by interlacing chromatin network ; 

1 Regarding the cell membrane, it is well to know that this is a purely relative _ term, just as a 
drop of chloroform in water, or a drop of water in chloroform, or a bubble of air in water, can 
be said to have a cell membrane. These are really surface tension phenomena, where the inter- 
phases of water-chloroform, etc., have equal resistance to each other. In the "cell membrane" we 
really have naked protoplasm, tending to round up just as the drop of water does in chloroform. 

The Cell 


(g) Centrosome, a small spherical body often found in the cyto- 
plasm of animal cells near the nucleus. It is looked upon as the dynamic 
center in cell division. 

If the student is to study Medicine he will probably find an advan- 
tage in dividing the various definitely discernible substances in the 
cytoplasm, into Mitochondria, Plasmosomes, and Paraplasmic sub- 

Mitochondria 1 (Fig. 27). These are little granules, rods, and threads 
in the protoplasm, quite constant in the various cell bodies, at least, of 
the animal world. In fact, one investigator insists that it is these 
mitochondria, rather than the chromosomes, which are the bearers of 
heredity; while another insists that they accumulate at both poles of the 
cell, and are converted into secretory granules. 

Plasmosomes. 2 These are tiny granules distinguished from the 
mitochondria because they are concerned with the housekeeping of the 
cell, that is, with the assimilation of food materials, with forming various 
secretions, and with the excretion of waste matter. Plasmosomes have 
not been seen, but are supposed to be present because certain substances 
are produced in the cells which must be due to something physical or 

Fig. 27. Mitochondria as they appear in the Sex Cells of Dividing Sperm of Blaps. 

a. Scattered granular mitochondria. 

b. Rod-shaped. 

c. Rods drawn out around spindle. (After Duesberg.) 

chemical. This is shown by the fact that the products of the cell form 
little swellings of various kinds. These swellings take a stain, and 
it is the particles which cause these swellings, or cell-products, which 
are known as plasmosomes. The cell-products consist largely of fat 
and carbohydrates, and may be stored in the cells. Cell products are 
called cytofacts or metaplasm. (This latter term is applied because such 
substance is due to metabolism.) 

Golgi apparatus (Fig. 28). Very recently by a special staining 
method known as Golgi's silver impregnation method, it has been found 

1 While some medical men usually speak of mitochondria, and some of the older writers use 
the term bioplasts, plastidules, archoplasmic granules, plastosomes, plastochondria, chondrioconts, 
plastoconts and chondriomites, depending on the shape of the mitochondria, the name cytologists 
use is that of Chondrio somes, so that the student must think of mitochondria and chondriosomes as 
interchangeable terms. 

2 Medical men are inclined to use the term plasmosomes as here given, but cytologists use the 
term only to mean true nucleoli. These latter workers never use it in the sense we have given it 
in this book. 


General Biology 

that there is an "internal reticular apparatus" consisting of a system of 
rods or network close to the nucleus, but associated especially with the 
dense protoplasm which surrounds the centrosome. In epithelial cells 
the network lies close to the free ends of the cells. The Golgi apparatus 
is probably found in all animal cells, though little is as yet known about 
it, except that there is a continuity from parent-cell to daughter-cells 
by a sort of mitotic division of it quite similar to the regular chromosome 
division. Prolonged treatment with osmic acid will make the Golgi 
apparatus visible. 

Plastids are differentiated portions of protoplasm representing cer- 
tain regions in which physiological processes are localized. They are 
quite common in plants and protozoa. In the former they are usually 
colored, such as the chloroplasts which are the chlorophyl-carrying 
organs. Each kind of plastid is supposed to serve a separate type of 

Attraction sphere and Centrosome. These may be quite conspicuous 

Fig. 28. Golgi Apparatus in Epidermal Cells. 

a. Golgi network beside the nucleus in cell of a horse. 

b. Same in skin of cat, but broken into small rods around the mitotic figure 
in the large central cell. (After Deinecka.) 

although it is not known whether they are important or not in cell- 
division, shortly to be described. 

Paraplasmic substances. These are the foreign substances which 
can be seen in the cytoplasm, but which have not become part of the 
living cell itself. Such are granules of pigment or calcium, fat globules, 
various vacuoles filled with fluid, etc. 

"It is clear," says a recent writer, "that the construction of the cell 
is highly specialized in most cases for the function which it is to carry 
out, and that it is supplied with the most perfect mechanisms for these 
purposes. Some of these are evident in the form of contracted bands 
in the protoplasm, or in long, nerve processes ( ) 

like electric wires carefully insulated by sheaths of fatty material, or in 
mobile cilia which mechanically perform duties in the transportation 
of foreign particles. In others, the tools of their trade are recognizable 

The Cell 93 

in the form of the granules which seem to prepare ferments by which 
the chemical processes which the cells effect are carried out. While 
these are visible in many cases, there are others, even when we know 
that the most multifarious chemical reactions are being carried on, in 
which nothing of the mechanism is recognizable to our eyes." 

In plant cells where the cell wall is quite thick, and in some of the 
animal cells, this cell wall is made up of cellulose, a substance quite 
clearly related to the starches, although there are other substances, such 
as lignin or silica, often associated with it, while in the cell walls of 
animals there is a nitrogen containing substance, such as chitin, keratin, 
and gelatin. 

Where there is no distinct cell wall, there may be a cuticle, or 
pelicle, covering the entire cell. This may be considered a lifeless 
secretion just the same as is the cell wall produced by some of the vital 
activities of the cell itself. The vacuoles are little open spaces or vesicles 
of liquid enclosed within the protoplasm. They may be persistent or 
merely temporary. Vacuoles are quite common in protozoa. If they 
enclose food particles they are called food vacuoles. They may, by con- 
tracting suddenly, eject their contents and serve thus as excretory organs. 
As these vacuoles which eject their contents usually are formed again 
in the same place, they are called pulsating or contractile vacuoles. 



ORGANIC CHEMISTRY, although named after the organs of 
living things, has come to be the study of carbon compounds. 
But as the three great chemical groupings of a living organism 
consist of proteins, carbohydrates and fats and all of these contain 
carbon, a large part of the study of organic chemistry is still devoted to 
living matter. 

One of the great problems of Biology is to solve the riddle of how 
and where life originated. If the stars and planets surrounding our 
globe were at one time masses of intensely heated matter, no life could 
have been sent from one planet to another. Still it is interesting to 
know that the first elements appearing on a cooling star are the very 
ones which go to make up proteins ; namely, carbon, oxygen, hydrogen, 
nitrogen, and sulphur. 

It will be remembered that oxygen is the source of most of the 
energy of an organism, and that the cell is the unit of Biology, this cell 
being made up of various substances called protoplasm. 

If a substance is of the consistency of glue and non-crystalloid, 
it is called a colloid. 

Colloids are contrasted with crystalloids, such as sugar, salt, urea, 
etc., in fact, any of those substances which, when in solution, will pass 
through a membrane. 

An emulsion is one fluid phase suspended in another. The fluids are 
said to be in suspension. 

Most organic matter is colloidal, and some biologists believe that a 
colloid substance v/ill ultimately be accepted as the biological unit in 
place of the cell. 

Protoplasm, the substance of the entire cell, has somewhat the form 
of foam, although it differs from foam in having the alveoli filled with 
a thick liquid substance about the consistency of the white of an tgg. 
The alveoli which make up the foam-like protoplasm, although having 
very thin walls, have walls thick enough so that diffusion is very slow 
and the substance itself is different in the alveoli themselves and the 
spaces between the alveoli. 

All protoplasm does not show such alveolar composition. With the 
ultra-microscope much of the protoplasm appears as tiny particles. It 
is, therefore, supposed that this homogeneous mass is colloid in char- 
acter, that is, consists of tiny granules which are suspended in a liquid 
medium. As there is not much difference between a colloid and an 

Chemistry of Living Matter and Cell Division 95 

emulsion in this case, and as there are cases in which no alveoli can be 
seen, it is possible that alveolar substance and interalveolar substance 
may differ about as much or as slightly as a colloid and an emulsion. 

The early workers on the cell saw very thin fibers in the proto- 
plasm, and established the "filar" or "reticular" theories of protoplasmic 
structure. We now know that, if the alveoli are arranged in rows, the 
liquid between the alveoli will appear like threads, although we have 
not been able to find that these so-called fibers have any important 
function. These theories, therefore, are not among the important bio- 
logical problems of the present time. 

When cells are prepared and stained for study in the laboratory, 
they have many granules distributed within them. These may be coagu- 
lation products of the interalveolar protoplasm or, the cut ends of fibers 
or cell inclusions of various kinds. 

The great mass of protoplasm is really an emulsion. The tiny 
bubble-like particles, or alveoli, and the liquid in which these float are 
called by the physical chemist "phases" of a "system." It can, therefore, 
be understood that the various surface phenomena which interest the 
physical chemist are to be found in the living cell, and any chemical 
knowledge of this nature, which the student of the cell can obtain, will 
stand him in good stead. Much of the activity of protoplasm can be 
explained by a study of surface tension. 

It is to be borne in mind that protoplasm is never solid, although 
solid particles may be, and most often are, included within its liquid or 
semi-liquid mass. 

Protoplasm is made up of both organic and inorganic substances. 

A. Always present. 


Intermediate products of metabolism. 
B. Not always present. 

Aromatic compounds, 
Toxic compounds. 1 
The enzymes are continually attempting to produce an equilibrium 
in the cells. They are chiefly protein in nature and speed up the chemical 

1 lt is, of course, to be understood that a substance is not toxic to the individual in the normal 
state. For example the poisonous sting of a bee or the poison gland of a rattlesnake is not toxic to 
the respective animal but to others. 

96 General Biology 

reaction. They may be killed by light or heat. Their activities are 
specific, each type of enzyme doing only one particular type of work. 
Every step in the breaking down of proteids is done by a specific 


A. Always present, and called essential constituents. 

C, O, H, N, Ca, Na, K, Cs, Fe, Mg, H,0, NH 4 , CO,, SO + , PCX. 

B. Sometimes present. 

I, Br, NO,, NO.,, Zn, Ba, Cu, Mn, As, F, Si, Al. 
Muttkowski has summarized the chemical constituents concerned in living 
matter as follows: 

I. Constituents concerned with food. 

1. Those which compose food. 

A. Proteins—C, O, H, N, (S, P)— build protoplasm. 

B. Fats — C, H, O — energy and reserve. Certain P-fats enter into 
building up of all protoplasm (lecithin). 

C. Carbohydrates — C, O, H — furnish the energy and reserve in pro- 

2. Constituents concerned in food synthesis. 
Mg, CO, (in plants only). 

3. Concerned with food storage — K. 

4. Katalysts — Fe, Ca, Mn, I. 

II. Constituents concerned with Physiological Processes. 

1. Regulation (turgor, toxicity) — K, CI, Na, Ca, I, Br. 

2. Sensory — P. 

III. Constituents concerned with Structural Relations. 

1. Form relations — elasticity — N, CI. 

2. Supporting tissues — C, Ca, Si, Mg, P, Fl, (S) in form of phosphates, 
carbonates, oxalates. 


Every living thing, plant or animal, begins its life as a single cell. 
Therefore, it follows that, if one wishes to understand how a many-celled 
animal (metazoan) ( ) comes to its adult form of 

life, one must find an original single cell and follow it throughout all its 
changes until it has come to adultship. 

Every living cell grows if it obtains food, and, when it reaches its 
maximum size, splits in two. It may do this equally or unequally; that 
is, it may split into a very large and a very small part, or it may split 
equally into halves of like size and shape. There are then two cells 
where there was only one before. These two cells then grow until such 
time as they attain their maximum size when the same process is gone 
through again, so that in a short time there are four cells, then eight, 
sixteen, thirty-two, sixty-four, one hundred twenty-eight, and so on. 

It is easy to understand what a division of cells may bring about 
when an old children's story is recalled. According to this story, a 
blacksmith expressed his willingness to shoe the King's horse on Sunday 
provided the King would pay one cent for the first nail, and double that 
amount for each additional nail. By the time the blacksmith had driven 
in the twenty-eighth nail, he had won more than a million dollars for 
the last nail alone. In the case of the tiny bacteria, which are single- 

Chemistry of Living Matter and Cell Division 


celled plants, the division and increase may take place every few minutes 
so that in the course of a few hours there are millions upon millions of 
cells where before there was only one. 

Writers on Biology commonly hold that there are two ways in 
which cell division comes about, but recent investigations tend to show 
that this may be erroneous and that all cell division is probably mitotic. 
One method is said to be the shorter and simpler way, in which the cell, 

Fig. 29. Diagrams Representing the Essential Phenomena of Mitosis. 
A, resting stage; B, early prophase; C, late prophase; D, mesophase ; E, metaphase ; F, end 
view of E; G, anaphase; H, late anaphase; I, telophase; J, late telophase. 


1, centrosome. 7, cytoplasm. 

2, attraction sphere 8, cell wall. 

(centrosphere). 9, vacuole. 

3, nuclear membrane. 10, astral ray. 

4, nucleolus. 11, spireme. 

5, nucleoplasm. 12, aster. 

6, linin network and 13, spindle. 


(Redrawn from Jewell Models, by permission of General Biological Supply House, Chicago.) 

14, chromosome. 

15, central spindle fibers. 

16, mantle fibers. 

17, beginning of new cell wall. 

18, chromosomes breaking down. 

19, spindle remnants. 

20, new cell wall. 

without any previous changes that could be observed, splits in two parts. 
But the longer method, known as mitosis (Fig. 29), is the more com- 
mon, and is the one which must be studied in detail if any understanding- 
whatever is to be obtained as to how plants and animals evolve from 
the single original cell into the marvelous, complex organisms of adult 

The cell, as described in the last chapter, has a network in the 
nucleus that stains quite easily and readily. When this network is not 
in the process of division the cell is said to be in the resting stage. In 
the higher forms cell division takes place only after fertilization, that 

98 General Biology 

is, after the male sperm has united with the female egg. The chromatin 
(stainable nuclear network) begins a process by which the stained part 
separates from the rest of the network, taking upon itself the shape of 
a single thread or skein. A little later, this skein of chromatin breaks 
up into small particles of various shapes. Some of the more common 
shapes are those bent like a horseshoe or like the capital letter L, and 
those that appear as little straight or bent rods. Such portions of 
chromatin are called chromosomes. As these chromosomes are in all 
probability the most important physical particles in the study of Biology, 
one must get this subject of mitosis and chromosomes clearly in mind 
or all that follows will be lost. 

Just before the cell goes from the resting stage into the skein or 
spireme stage, the little centrosomes lying within the centrosphere break 
into two parts, one part migrating around the nuclear wall until it lies 
opposite the first half. 

Formerly it was thought that it was due to these centrosomes that 
the chromatin breaks up into chromosomes, but as no centrosomes are 
found in higher plants, although the chromatin acts just as it does in 
animal cells, this explanation must be given up. Between the two 
centrosome parts in the animal cell there develops a series of very fine 
lines, which may be only a reflection of some kind, but which are very 
frequently seen when the cell is undergoing mitosis. These fine lines 
are called a spindle, readily recognized in the drawing. Four periods in 
cell division are usually mentioned : 

The Prophases. This is the skein stage already referred to. 
The Metaphase. Immediately after the chromosomes have appeared 
as small broken particles of chromatin, they gather at the mid-line or 
equatorial region of the spindles. Then the chromosomes split in two 
lengthwise, and the cell is said to be in the metaphase stage. 

The Anaphases. Immediately after the chromosomes have divided 
lengthwise, one-half of them move toward one polar body and the other 
half toward the other. During the time the chromosomes have split 
and the time they have united about the centrosomes, the cell wall has 
indented until it meets the opposite indentation, thus forming two sepa- 
rate daughter cells. 1 This stage is called the anaphase. 

The Telophases. This phase lasts from the anaphases until the 
time the cells again resume the resting stage. 

It will be noted that the metaphase is used in the singular, whereas 
the other three have been used in the plural. This will be readily under- 
stood when it is remembered that these terms are only convenient names 
enabling us to discuss intelligently with others the whole subject of 
mitosis, and, so that when a given thing or event is observed during 
any particular time of the division of the cells, it can be written and 
spoken about in an understandable way. 

The metaphase is only that particular moment when the chromo- 

x In plants a new cross cell-wall often originates by a thickening of the central spindle fibres. 

Chemistry of Living Matter and Cell Division 99 

somes have gathered at the equatorial plane and are then separating. 
All the other phases cover a much longer period, and as they pass 
through various stages, are therefore used in the plural. 

In different types of cells, all of these stages vary a little as to length 
of time and as to the method in which and by which particular cen- 
trosomes, skeins (also called spiremes), spindles, and chromosomes, 
arrange themselves. It is well to note that in the higher forms of 
plants, centrosomes have not been seen, and that there is a difference 
between plants and animals in the way the cytoplasm divides. In the 
animal cells, as shown in the drawing, the cell walls indent until the 
two indented portions meet, and the separation takes place in that way; 
whereas, in the plant cell the cell-wall does not indent, but the wall 
becomes thicker and thicker until a definite cell-wall has been grown 
for the two new cells. 

There are exceptions as to just when and how the spindle forms. 
In some species of salamander, the spindle begins outside of the nucleus, 
and then, as the nuclear membrane disappears, the fibers pass through 
the nucleus itself. 


The real significance of mitosis is found in the fact that the chromo- 
somes (a more detailed study of which will be taken up as soon as the 
protozoa have been studied) split in two lengthwise and that the chromo- 
somes are practically the only known visible carriers of characteristics 
that pass from a parent cell to become a new individual. Whatever an 
offspring is to obtain from its parents must, therefore, be already present 
in the chromosomes of the various germ cells of the parents, or it cannot 
be inherited by the offspring. 

A little later it will be explained how the lengthwise dividing of the 
chromosome means that each new individual obtains one-half its chro- 
matin matter from each parent. As the chromosomes carry the factors 
which produce the various characteristics each individual possesses, it 
follows that each new individual receives one-half of his various charac- 
teristics from the father and one-half from its mother, although 
usually these are not evenly distributed as to quantity, and possibly, 
quality. For example, we may, so far as external appearance go, resem- 
ble our fathers, yet have our mother's mental characteristics. One must, 
therefore, not confuse the characteristics which can be seen and are very 
conspicuous, with those which may not be seen, but which may never- 
theless be much more important. 

By remembering this statement one may understand the biologist's 
division of all cells in the body into two great groups. These two 
groups are known as somatoplasm ( ) and germplasm 

( ). The latter consists of those particular cells 

which will reproduce offspring like the parent, while the somatoplasm 
consists of all the other cells of the body. It can be imagined from 


General Biology 

this that it is quite possible for the somatoplasm, or outer portion of 
the body (which is the only portion visible), to cover up many important 
or, at least, latent and dormant characteristics which an individual 
may have inherited, but which characteristics may come forth at any 
moment. In fact one can understand that such characteristics may lie 
dormant throughout the entire life of a parent and come forth only in 
the offspring. 


Very low in the scale of life 



I 24) 

ReducNon I 


Meiol-.c • 
division ; 

Posr meiofic 



Cerm cells ( 

D © 0, 


or Zygote 


Ordinary ', 

° r < 

( 24 

divisions i 

Fig. 30. 

A. Diagram illustrating the behavior of the 
"accessory," sex-accompanying chromosome in 
fertilization. For the sake of clearness, but 
four other chromosomes are shown, and these 
four diagrammatically; accessory Or), solid 
black. (After Wilson.) 

B. A diagram of the gametogenesis and 

there is a differentiation into sexes ; 
the smaller, more active particle is 
known as the male gamete, while 
the larger, passive portion is the 
female gamete. 

In all higher forms fertilization 
is our starting point in any discus- 
sion of embryology or development. 

There are apparent exceptions 
to this rule, such as those insects 
which give rise to young by virgin 
birth, a process called parthe- 
nogenesis ( ), and in the 
case of those animals in which sev- 
eral (as high as three) immature 
generations may be present at the 
time of birth. This latter condition 
is known as paedogenesis ( ). 

Before fertilization, various 
changes take place in the germ cells 
which are to produce the mature egg 
and sperm. This process is called 
maturation ( ), (Fig. 30). 

The early cells are called pri- 
mordial germ cells. They are in a 
state of rest in all the higher animals 
for several years, or until the indi- 
vidual grows to sexual maturity. 
When this time has been reached, 
there are three stages through which 
the primordial cell passes before 
producing the mature ovum or 

1. The primordial germ begins 
to divide mitotically (Fig. 31). The 

resultant cells are called oogonia and spermatogonia. 

Chemistry of Livixg Matter and Cell Division 


sperm\ 9 egg 

\ / 


2. After a varying number of divisions, the many new cells thus 
produced go through a process of growth. They are then called primary 
oocytes and spermatocytes. 

3. These then "ripen" or "mature," after which fertilization can 
take place. 

From what we shall soon learn regarding Paramoecia we know that 
the chromosomes are the important carriers of all physical traits inher- 
ited by a child from the parent. But, unless there is some method by 
which the chromosomes throw off one-half their number, each child, 
being the result of an egg and a sperm mating, would possess every- 
thing its mother possessed, plus everything its father had. A super-race 
would thus be produced which in a very few generations would be 
totally unlike any of its parents. One can imagine what it would mean 
to have every child twice as strong, and twice as tall, as its parents. 
It would not be long before men would be thousands of feet tall, and 
there would be little room for more than one or two people in the world. 
But nature apparently loves an average, and so somewhere, the chromo- 
somes are halved. 

The ripening process is known as 
the maturation division (Fig. 30). 

The egg varies from the sperm in 
the number of complete functioning 
cells it produces, although the chro- 
matin acts alike in both cases. 

From the primordial egg cell only 
one mature egg develops, while three 
undeveloped eggs, called polar bodies, 
are formed. These latter degenerate 
and have no known function. Each 
sperm cell, however, develops into 
four complete functional spermatozoa, 
any one of which may fertilize an egg. 

Notwithstanding this difference, 
both sperm and egg cell have the same 
number of chromosomes characteristic 
of the species. This full quota of 
chromosomes is called the diploid 

The primordial cells (those which 
are to become eggs) begin their growth 
very early in the embryo. Usually, a 
quantity of yolk is deposited to serve 
as food for the embryo which is in turn 
to develop from the egg. 

The chromatin in the nucleus 

Fig. 31. 
A. Diagram of the derivation of the sex 
cells. z., the fertilized egg (zygote) ; 
som., the body plasm (soma) ; t., the de- 
velopment period during which the germ 
plasm and the body plasm are indistinguish- 
able; sp., spermary; ov., ovary; p., primor- 
dial germ cells; u., the period of rapid in- 
crease in number and diminution in size 
(the number of divisions is much greater 
than shown) ; v., the period of increase in 
size with differentiation of cytoplasm; w., 
the two maturation divisions; ph., polar 
bodies; e., egg. (After Boveri.) 
B. Spermatozoa of Rena esculenta. mp., 
middle piece. 

C. Spermatozoa of Rana fusca. (After 


General Biology 

gathers in a thick mass towards one side of the nucleus. This is known 
as the synapsis stage. From this thick mass of chromatin there will 
emerge just one-half the number of chromosomes usually found in cells 
of the particular species we are studying. Such cells are said to have 
the haploid number of chromosomes. 

Each of these chromosomes is double, the two parts either lying 
side by side, or end to end. This stage of half the number of chromo- 
somes (but where each is a double chromosome), is called pseudo-reduc- 
tion. Real reduction then follows. The two parallel portions of each 
chromosome divide longitudinally, while the entire chromosome con- 
tracts into small four-portioned chromosomes, each of which is called a 
tetrad (Figs. 31 and 33). A mitotic figure now forms and moves toward 


Fig. 32. Fertilization of the Amphibian Ovum. 

A, outline drawing of a section parallel to the axis of the egg; the superficial 
pigment of the animal hemispheres of the egg is indicated, but the yolk granules 
are omitted, co., entrance cone; spz., spermatozoon lying at the bottom of the 
entrance funnel; s.sp., spermsphere. 

B., a meridional section through the egg at a later stage; cf, sperm nucleus, 
also called the male pro-nucleus; $, egg-nucleus, also called the female pro-nucleus; 
as., sperm-aster; ph., polar body. The size sperm-and egg-nuclei has been exag- 

C, portion of a section through an egg showing an early stage in the forma- 
tion of the fertilization spindle, highly magnified; d" sperm-nucleus; $, egg- 
nucleus; cs., centrosomes. 

D, portion of a section of an egg showing the early stage of the metaphase of 
the fertilization spindle; chr., the chromosomes derived from the sperm-and egg- 
nuclei lying unevenly, but still in two distinct groups, in the equatorial plane. 
(After Jenkinson.) 

the outer rim of the egg. The nucleus divides equally, so that one-half 
of each tetrad passes to a daughter nucleus. 

Although the nucleus divides equally, the cytoplasm does not. This 
produces one large egg cell and one small particle, this latter with one- 
half the chromatin, but with little or no cytoplasm. The smaller portion 
is the first polar body. This is pinched off from the egg cell proper. 

Both egg cell and polar body now begin to divide again. It is in 
this second division that each remaining half-tetrad (now called a dyad), 

Chemistry of Living Matter and Cell Division 


separates into its two component parts, one going to each daughter 
nucleus. Thus the second polar body is formed which is also pinched 
off from the egg cell proper. Often the first polar body again divides to 
form two tiny cells, but none of the polar bodies perform any actual 
known function for the organistn. From this account we note that 
four cells have formed from the primordial egg cell — the egg propel 
and three polar bodies. Two of the polar bodies are the result of me 
first polar body dividing in turn. / 

It is of great importance to note that the order of development may 
change in different species. For example, some polar bodies never 
divide, while in some species maturation takes place before, and/m others 

after fertilization. / 

We shall see in oar study of 
plants that this reduction-division is 
not confined to the animal world. 

The male ceJf — the sperm — 
passes through^ similar changes to 
that described for the egg cell, ex- 
cept that there are no polar bodies 

In Biology we always think of 
the reproductive cells as the germ 
plasm which alone carries on from 
parent to offspring all things that 
can be inherited. It must, therefore, 
follow that there is something in the 
germ plasm which determines what 
the offspring is to be. These de- 
termining factors must be in the 
chromosomes because it is only the 
chromosomes which pass from par- 
ent to child. But there can be a con- 
siderable "change-about" of the 
chromosomes. For example, if we 
have four chromosomes numbered 
1, 2, 3, 4, either 1 and 2 may be 
thrown out in the reduction division, 
thus leaving 3 and 4; or 1 and 3 may be thrown out, leaving 2 and 4; 
or 2 and 3 may be thrown out, leaving 1 and 4; and so on. 

If it be remembered that quite a number of combinations can be 
made in this way in both the egg and the sperm, it is readily understood 
that several times this number of combinations can be brought about 
by a mingling of sperm and egg after fertilization, when the reduced 
sperm cell unites with the reduced egg cell. When we come to the study 
of Genetics, we shall enter into this phase more thoroughly. 

Fig. 33. Maturation of the Egg of Cyclops 
(the full number of chromosomes is 
not shown). 
A, chromosomes already split longitudinally; 
B, chromatin masses with indication of trans- 
verse fission to form the tetrads; C, the young 
tetrads arranging themselves- on the first polar 
body spindle; D, tetrads in first body spindle; 
E, separation of the dyads in the same; F, 
position of the dyads in the second polar body 
spindle, the first polar body being really above 
the margin of the egg. (After Ruckert.) 

104: General Biology 

It will, of course, depend upon what characters are thus carried by 
the two mating chromosomes as to what characters the new organism 
will possess. It is this assorting and rearrangement of chromosomes 
which is in all probability the cause of variations within a given species. 
This is by no means the same as saying that it is the cause of new 
species. This distinction must be kept clear. 

The diploid number of chromosomes is reduced to the haploid num- 
ber by a union of the chromosomes, two by two, as already stated. But 
this union in groups of two is by no means haphazard. An understand- 
ing of this can best be seen in animals where the chromosomes are 
different both as to shape and size. The squash-bug (Anasa tritis) is a 
good example. 

In these bugs the chromosomes occur in two sets, larger ones and 
smaller ones (Fig. 30). During pseudo-reduction, the larger unites with 
a larger one, and the smaller with a smaller one, and so on. All the 
resulting tetrads are symmetrical. 

The sum total of all the character-factors, which are received from 
the parents of an animal at the time the egg is fertilized, are contained 
in these two sets of chromosomes. In some insects virgin birth is not 
uncommon. In these cases a complete individual develops from the 
mature egg alone — that is, from the one having only one-half the definite 
number of chromosomes normally present in each cell of that species. 
This shows that each set of chromosomes contains all that is necessary 
for a complete individual. We, therefore, think that the linking of a 
similar chromosome from the male and a similar one from the female 
must be for the purpose of bringing similar important factors together 
so as to strengthen such factors. A fuller discussion of inheritance will 
be left for the chapter on genetics. 


The union or fusion of the sperm nucleus and the egg nucleus is 
known as fertilization ( ). The spermatozoon is 

composed of three parts, head, tail, and mid-piece (Fig. 31). The head 
is largely nuclear material and is the only portion which actually enters 
the egg and fuses with it. Sperm may enter an egg either before or 
after maturation of the egg is completed. 

After the sperm cells have passed through the maturation process 
a great mass of them are secreted at one time from the spermaries. If 
an animal lives in water, the sperm float about in that fluid, otherwise 
enough liquid is excreted to make it possible for the sperm to float about 
until coming in contact with an egg. 

Among all higher animals there are special copulatory organs which 
vary considerably in different animals but which, in all cases, serve to 
bring egg and sperm together. 

There is a great attraction between these germ cells of the different 

Chemistry of Living Matter and Cell Division 


sexes which cause their union and fusion, though what this attraction 
is has not yet been discovered. 

If the sperm enters the egg after the latter has matured (which 
is by far the more common method) certain changes begin taking place 
at once. 

The sperm nucleus is called the male pronucleus (Fig. 32) after it 
enters the egg, while the nucleus of the egg is known as the female pro- 
nucleus. There is often a special aperture in the wall of the egg, called 
a micropyle, ( ) through which the sperm enters. 

Usually only one sperm cell enters an egg. Various changes are set up 
at the very moment the sperm enters the egg, causing the egg membrane 
to become impervious to other sperm. Sometimes, if the egg be old or 
diseased, this process may not begin soon enough, so that several sperm 
enter the same egg. This is called multiple fertilization. There are 

O © 

A, one-celled stage B, two-celled stage C, four-celled stage D, eight-celled stag« 

B, sixteen-celled 

H, many-celled 

Fig. 34. Cleavage of Frog's Egg. 

some species in which this multiple fertilization occurs normally. Mon- 
strosities are often formed in this way. 

When the two pronuclei unite, they form a fusion nucleus (Fig. 32), 
also called the first segmentation nucleus. The egg is then said to be 
fertilized, or impregnated. 

The full quantity of chromosomes is now again present, and there 
seems to be an impulse brought with them which starts the egg dividing. 
This division of the fertilized egg is known as segmentation or cleavage 
(Fig. 34). This is brought about by ordinary mitosis, and these first 
cells, which come into being by the splitting of the fertilized cell, are 
called blastomeres ( ). The chromosomes do not 

divide longitudinally in these blastomeres, but each new cell receives 
one-half of the material brought by each of the parent cells. In this 
way every cell in the body gets an equal amount of chromosome mate- 
rial from each of its parents. And in this way also, every cell in the 
body of an individual has exactly the same number of chromosomes 
within it that every other cell has. 

Each succeeding division of cells produces cells a trifle smaller than 
the parent cell. 

The cells divide differently with different quantities of yolk. 
Usually the first three cleavage planes are perpendicular to each other. 


General Biology 

If the yolk is evenly distributed, the newly formed cells will be more or 
less of equal size. 

Often the yolk collects at the lower portion of the egg. This is 
undoubtedly due to the force of gravity. In such cases the protoplasm 
gathers at the upper end. The upper end is then called the active, 
formative, or animal pole and the lower the passive, nutritive, or veg- 
etable pole. The polar bodies are usually freed at the formative pole. 
This causes the blastomeres at the nutritive pole to become larger, and 
divide less rapidly than those in the region where there is an excess 
of protoplasm. In fact the yolk may be so excessive as not to permit 
any division at all within it. 

Two forms of segmentation are usually given: 
A. Total segmentation. 

I. Equal: In which there is little yolk material and that 
well distributed. (Illustrated in most of the lower invertebrates and 

II. Unequal: In which a moderate amount of yolk accumu- 
lates at the passive pole. The cells at the active pole are more numerous 
and smaller than at the passive. (Illustrated in many mollusks and in 


Partial segmentation. 

I. Discoidal: In which there is an excessive amount of yolk 

with the nucleus and a small mass of 
protoplasm occupying a disc at the 
active pole. This disc alone segments, 
and the embryo lies upon the yolk. 
(Illustrated in the eggs of fishes, birds, 
and reptiles.) 

II. Peripheral: In which an 
excess of yolk collects at the center of 
the ovum, with the protoplasm at the 
periphery. The dividing nuclei assume 
a superficial position and surround the 
unsegmented yolk. (Illustrated in the 
eggs of insects and other arthropods.) 

c J> 

Fig. 35. 
A, vertical section through a segmenting 
ovum in the blastula stage. B, C and D, 
similar sections through later stages. BL, 
segmentation cavity or blastoccele; bp., 
blastopore. (After Morgan.) 


As segmentation continues the 

blastomeres remain attached to each 

other and form a spherical mass (Fig. 

35). If the individual cells project out from the mass and the sphere is 

more or less solid, it resembles a mulberry and is called a morula 

Chemistry of Living Matter and Cell Division 


( ), but if it becomes a single layer of cells and is 

hollow, it is known as a blastula ( ). In the latter 

case the hollow portion in the center is rilled with a fluid. The hollow 
space itself is called the segmentation cavity. 

If this blastula indents (just as though one were to take a hollow 
rubber ball and push in one side with a ringer), there are two layers 
in the indented region. The outer layer is called the ectoderm or epiblast, 
and the inner the entoderm, endoderm, or hypoblast, while the entire two 
layered mass is known as a gastrula ( ). The 

indentation is also called invagination and gastrulation (Fig. 36). 

Having indented, the indented portion draws together to form a 

single mouth-like opening. This open- 
ing is the blastopore ( ), 
and the newly made cavity surrounded 
by entoderm is the primitive intestinal 
tract or archenteron ( ). 
In our study of the hydra it will be 
found that that animal grows thus far 
and then remains throughout its entire 
career in the gastrula stage. 

In higher forms a third layer is 
formed between the ectoderm and en- 
toderm known as the mesoderm. Ani- 
mals having these three germ layers 
(Fig. 37) are called triploblastic 
( ). All tissues 

and organs are derived from some one 
or more of these germ layers. To 
study this development is the special 
province of Embryology. 

Often certain blastomeres grow 
more rapidly than others in the same 
embryo. Such is the case with frog's eggs (Fig. 38). This results in 
the more rapidly growing cells surrounding those which divide more 
slowly. A growing of one set of cells over another is called epibole 
( ). The separation of the germ layers or mem- 

branes by splitting apart is known as delamination. 

Fig. 36. Formation of the Gastrula in 
Amphibia. Diagrammatic Longi- 
tudinal Section. 
1, Blastula; 2, the invagination has be- 
gun at i (the corresponding place in 1 is 
indicated by an arrow) ; the invagination 
is in the form of a furrow, but does not 
yet surround the egg; 3, the invagination 
is proceeding; 4, perfect gastrula; the 
archenteron is almost filled with a project- 
ing part of the hypoblast, which is later 
dissolved and absorbed by the embryo, ek., 
ectoderm (light) ; en., entoderm (shaded) ; 
g., mouth of gastrula; h., segmentation 
cavity; %., invagination furrow; »., archen- 
teron. (After Boas.) 

Fig. 37. Diagrammatic Figures in Explanation of the Formation of the 

Third Germ Layer — the Mesoderm. 
1, youngest, and 4, the oldest stage. 

ek., ectoderm; en,, endoderm; m,, mesoderm, (After Boas). 

Fig. 38. Frog's Egg, 
Showing Proportion- 
ate Increase of 
Smaller Cells at 
Top of Egg. 

108 General Biology 


E. W. MacBride, "Textbook of Embryology." 
E. B. Wilson, "The Cell in Development and Inheritance " 
Kellicott, "Chordate Development." 
Gurwitsch, "Morphologie und Biologie der Zelle." 
. Heidenhaim, "Plasma und Zelle." 
Buchner, "Prakticum der Zellenlehre." 
L. W. Sharp, "An Introduction to Cytology." 

W. E. Agar, "Cytology, with Special Reference to the Metazoan 

L. Doncaster, "An Introduction to the Study of Cytology." 



EVERY living individual, plant or animal, which is able to live an 
independent existence and which possesses the four characteristics 
of irritability, ability to take and digest food, to grow by intus- 
susception, and to reproduce its own kind, is called an organism. 

The higher organisms are made up of separate specialized organs, 
each organ consisting of a series of tissues, and each tissue, in turn, 
made up of a sheet of similar functioning cells. 

The cell is the biological unit, and the modern world attempts to 
explain all living things in terms of cellular construction. 

It can be appreciated readily that the cell is intensely important 
in the study of all living organisms when it is realized that every living 
thing, plant or animal, originally grows from a solitary cell, and any 
tiny structure capable of producing so wondrous an animal as the frog 
or still more wondrous an animal as the human being, is certainly of 

In fact, if one could find all the possibilities of any given cell, and 
then find why it has these possibilities, and just how and why it 
develops into the particular structure that it does and no other, the 
riddle of life would be solved. 

It must be remembered that every living thing starts life as a single 
cell, and then, if it is to become a multicellular animal, it passes through 
a cell-dividing stage. Some plants and animals remain in the one-celled 
stage, while others, as soon as they begin to divide, adhere together and 
form tissues, which in turn develop into organs. This means that a 
study of the origin, development, and content of the unit cell gives us 
a sort of bird's-eye view of how living things work and grow. A study 
such as this presents a more complete view than could be obtained in 
any other way. 

First, therefore, it is necessary to know the different kinds of tissues 
that may be encountered. These are grouped under four distinct heads : 

1. Epithelial. 

2. Connective. 

3. Muscular. 

4. Nervous. 

1. Epithelial tissues (Fig. 39) are always surface tissues. They 
lie in layers with a small amount of intercellular substance. The sur- 
faces of organs, the linings of cavities of organs, and the lining of glands, 
blood vessels, and ducts of all kinds, possess this tissue. In fact, it is 


General Biology 

surface tissue whether lying on the internal or external surface of an 

There are, however, various types of epithelial tissue and these are 

named from their shape. 
For example : Flattened or 
squamous epithelium, easily 
obtained from the outermost 
skin of the frog during the 
time it molts or from the 
peritoneum, is composed of 
cells which are broad and 
flat with a rounded nucleus 
near the center. 

In the mucous layer of 
the intestine, we find what 
is known as columnar epi- 
thelium, because the cells 
are shaped like columns, 
while in many places such 
as in the outer skin, there 
are transitional stages be- 
tween these two types of 
tissues which have some of 
the characteristic shape of both flat and columnar epithelium. 

If these cells are several layers deep, they are called stratified 

Should they have tiny hairlike substances (called cilia) at their outer 
ends, they are known as ciliated epithelium. Ciliated epithelium may 
have almost any shape — columnar, cuboid, or flattened. Ciliated epi- 
thelium is found in the mouth, throat, parts of the peritoneal lining of 
the body-cavity, inner lining of the oviducts, in the mouths of the ciliated 
funnels of the kidney, in the ventricles of the brain, and, in very early life, 
even on the outer surface of the body. 

2. Connective tissue (Fig. 40) serves to support and hold together 
various parts of the body. In this type of tissue, the intercellular sub- 
stance is quite abundant as contradistinguished from nearly all other 
types, and it is interesting to note that nearly all of the connective tissue 
is derived from the middle germ-layer or mesoderm ( ). 

The intercellular substance changes in many ways. It may remain soft, 
or become fibrous and even change into bone. The principal types of 
this tissue are as follows : 

White fibrous connective tissue, most widely distributed, and easily 
obtained from the membranes connecting skin and body-wall. Under 
the microscope it appears as a clear gelatinous substance in which many 
fibrils are embedded. The fibrils are unbranched but have a character- 

Fig. 39. 

A, stratified epithelium from the oesophagus of the 
rabbit, seen in section. In the lower part of the figure 
the connective tissue and muscular layers are shown. B, 
squamous epithelium from the mesentery of the Frog, 
silver nitrate preparation; El, E2, goblet cells from the 
frog's mouth; Dl, D2, isolated ciliated epithelium cells 
from the frog's mouth; D3, an isolated ciliated cell from 
the gill of the mussel. C, columnar epithelium from the 
intestine of the frog- (From Bourne, after a drawing 
by Dr. E. H. Schuster.) 

Histology of the Frog 


istic wavy appearance; often they are united in bundles and run in all 
directions. A few yellow elastic fibers may be scattered among the 
white. These are always straight, however, and not wavy. If the tissue 
should be treated with acetic acid, the white fibers swell up and disap- 

Outer circumferejh 



.- Haversian or con* 
centric lamella. 

— Haversian canal. 

Interstitial lamella. 

Inner circumferen- 
tial lamella. 

Fig. 40. 

A. Elastic cartilage. 

B. Haversian system with one lacuna sketched. 

C. Segment of transversely ground section from shaft of a long bone, showing 
all lamellar systems. (From Bohm and Davidhoff.) 

pear. The yellow are not affected. The yellow fibers may also branch, 
and when cut they do not curl as do the white fibers. In the various 
spaces of the matrix ( ) connective tissue corpuscles 

or cells may also be found, varying in form and appearance, often united 
with neighboring cells to form an irregular network, the meshes of which 
are filled with intercellular substance. White fibrous tissue varies in 
consistency and texture in different parts of the same animal. The loose 
tissue which binds muscles together is known as areolar ( ), 

and is composed of sheets and strands intersecting each other in all 

112 Genekal Biology 

planes. It is areolar which forms the fascia for each muscle, and is 
modified into a tendon at the end. 

The looser tissue of the lymphatic glands is called adenoid 
( ) and is composed of an irregular network of 

sheets and strands which forms a fine meshwork of supporting cells. 

The various ligaments uniting the bones are formed of a dense and 
non-elastic variety of white fibrous tissue. White fibrous tissue is also 
found in the cutis of the skin, the submucosa of the alimentary canal, 
in the walls of the blood vessels, in the substance of glands, and in the 
capsules covering various organs. 

Adipose tissue is regarded as a form of connective tissue in which 
the cells have enlarged by being gorged with fat. The nucleus here lies 
toward one side of the cell, while the cell-wall and a thin pellicle of pro- 
toplasm surround the fat globule. 

Cartilage is a dense and massive variety of connective tissue. The 
predominant type in the frog is known as hyaline ( ), 

the matrix of which appears transparent and homogeneous 
( ), although it really consists of numerous fibers of 

different types which can only be observed after chemical treatment. 
The cells in this type of tissue are contained in little rounded spaces, 
or lacunae, scattered quite irregularly through the matrix. There may 
be two or more cells in one lacuna, which leads to the belief that the 
cells may have been formed quite recently by a division of the parent 
cell. An intercellular substance is deposited around each cell, there 
being a sort of partition grown between each of the cells which gradually 
increases in thickness and presses them farther and farther apart. The 
outer surface of the cartilage is covered by a thin layer called the 
perichondrium ( ). 

Hyaline cartilage is found at the ends of the bones of the limbs, 
between the spinal vertebrae and the ends of their transverse processes, 
at the tip of urostyle, in the pubis of the pelvic girdle, in the hyoid, and 
the cartilage of the larynx and of both ends of the sternum. It also 
forms the basis of the cranium and the central axis of the lower jaw. 

Calcified cartilage is that which contains a deposit of lime salts in 
the matrix. It is found in the pelvis of old frogs, in the suprascapula, 
and at the ends of the larger bones in the limbs such as the head of the 
humerus and femur. 

Bone structure is quite similar to that of cartilage and also contains 
cells embedded in a solid matrix. In bone, however, the matrix is made 
more firm by a deposit of carbonate and sulphate of lime. If the bone 
is immersed in acid so as to remove the lime solids, the histological 
structure of bone is quite like that of cartilage. It does not follow from 
this, however, that bone is merely calcified cartilage, for bone and 
cartilage differ from each other both histologically and chemically. 
Cartilage often is followed by bone, but when it is, the cartilage has 
been broken down and the bony tissue has taken its place. We speak 

Histology of the Frog 113 

of two types of bone, namely, compact, and spongy or cancellous. The 
former is firm and dense while the latter is composed of a comparatively 
loose arrangement of plates and parts, thus lacking the strength of com- 
pact bone. The spongy, or cancellous, type is found in the center of the 
vertebrae and to a small extent within some of the long bones. Bones 
such as the femur and, in fact, all of the long supporting bones in the 
body, must be rather compact. A cross section of any of these long 
bones will show the outer hard portion of a compact bone with an inner 
soft marrow and a thin surface layer over the outside, called the perios- 
teum ( ). This latter is quite similar in structure 
to the perichondrium surrounding cartilage. The arrangement of the 
layers in compact bone is concentric, and the layers themselves are 
known as lamellae ( ). These lamellae contain 
numerous lacunae in which the bone-cells proper are found. Fine 
branching tubes, or canaliculi, containing processes from the bone-cells, 
are given off from the lacunae and extend in all directions, often 
anastomosing ( ) with the neighboring canaliculi. 

Bones grow like trees in that successive layers are added to the 
outside. The cells forming the inner layer of the periosteum, known 
as osteoblasts ( ), are continually giving rise to new 

bone cells, which cause new layers of bony substances to be deposited 
between the periosteum and the old bone. New layers, however, may 
be added on the inner surface between the walls and the marrow cavity. 

Muscle tissue (Fig. 41) is composed of elongated cells, or fibers, 
united by connective tissue, as already mentioned. There are three 
types, the voluntary or striated, the involuntary or unstriated, and the 
automatic or branched, a sort of combination of the first two, known as 

The nonstriated fibers are rather simple in structure, commonly 
spindle-shaped with a single nucleus near the center, often elongated. 
The ends of the fibers may be branched, but are not usually so. The 
length of the fibers varies to a considerable extent. They may be very 
narrow, or short and comparatively thick. In the involuntary muscle 
fibers there is usually no cross striation, but one may find delicate longi- 
tudinal strands, called fibrillae, usually considered to be the contractile 
elements of the cell. The cell wall itself is thin and transparent. Non- 
striated muscles respond to stimuli quite slowly, being also somewhat 
slow to relax after the function has been performed. It is found particu- 
larly in those branches of the body where sudden movement is not 
required, such as in the muscular coats of the alimentary canal, in the 
walls of blood vessels, in various ducts, in the lungs, in the urinary and 
gall bladders, and around glands in the skin, and also in the iris and 
ciliary muscle of the eye. 

Striated muscle fibers are more complicated in structure than non- 
striated muscles. They possess several spindle-shaped nuclei scattered 
throughout the cell, each nucleus surrounded by a small amount of 


General Biology 

undivided cytoplasm ( •). There is a thin but well 

defined cell wall, called the sarcolemma ( ), best 

seen where the contents of the fiber are crushed or broken apart. 

Each fiber of voluntary muscle is regarded as a single cell with 
numerous nuclei scattered throughout its cytoplasm. In the early stages 
of development there is but one nucleus in each cell in the voluntary 
muscle, but as the fiber grows and the nucleus rapidly divides, while the 



Fig. 41. 

A. Smooth muscle fibers from the bladder of a Frog. 

B. Heart-muscle syncitium. 

C. Striated muscle fibers from the muscle of a cat. Q, cross discs separated 
from each other by interposed discs II, 12. zz shows the stripe in which granules 
are visible, h, is shown as a center-disc, situated within the cross-disc. (From 
Krause-Schmahl "Histology," by permission of The Rebman Co.) 

cytoplasm does not, there are naturally a number of nuclei within a 
single cell wall. 

There is here both a longitudinal and a cross striation consisting of 
alternate light and dark bands. Sarcostyles ( ), or 

fibrillae, which extend the entire length of the cell, are the cause of the 
longitudinal striations. These fibrillae, as in the unstriated muscle 
fibers, are the contractile elements. They are kept apart by a semi- 
fluid substance, called the sarcoplasm. The fibrillae themselves are 
arranged in bundles or muscle columns separated from each other by a 

Histology of the Frog 115 

thicker layer of sarcoplasm than is found between the fibrillae. The 
cross striation is due to the fact that the fibrillae really consist of seg- 
ments or sarcomeres ( )• The segments are 
separated from each other by a very fine dark line, called Krause's 
membrane. This membrane extends not only across the individual 
fibrillae but across the entire sarcoplasm between the fibrillae of the 
fiber. Krause's membrane is bordered on each side by a more or less 
clear and lightly stained band formed by the ends of the two adjoining 
segments. The middle portion of each segment forms a so-called dark 
band, and across the center of this band there extends a second very 
delicate membrane known as the line of Hensen. Should the muscle 
fiber be cut transversely, the cut ends of the muscle columns present a 
number of polygoneal areas, known as Cohnheim's fields. The spaces 
between the fields are filled with sarcoplasm, and the dotted appearance 
is due to the cut ends of the tiny individual fibrillae. 

The muscle fibers of the heart are different from either the striated 
or unstriated fibers, although heart muscle does present cross striations, 
and, as in ordinary striated muscle, each fiber also possesses more than 
one nucleus. Further, every heart muscle cell has branches which con- 
nect with other branches, thus forming a continuous network, called a 
syncitium ( ). (A syncitium represents a group of 

cells whose separating walls or membranes have been lost, reabsorbed, 
or failed to form.) 

4. Nerve tissue (Fig. 42) is made up of nerve fibers and ganglion 
cells ( ). A nerve cell, together with all of its 

processes, is called a neuron. Each nerve is made up of a bundle of fibers 
held together by connective tissue and surrounded by a common sheath. 
The central strand of a nerve fiber is called the axis cylinder. About 
this is found the medullary sheath ( ), (also called 

the white substance of Schwann), then a delicate external membrane 
called the neurilemma or sheath of Schwann. 

There are various constrictions to be seen in any long nerve. These 
are known as the nodes of Ranvier. It is at these nodes that the white 
substance is interrupted although the axis cylinder and neurilemma 

The nuclei surrounded by a small amount of protoplasm are found 
immediately beneath the neurilemma. There are also various oblique 
markings across the medullary sheath between the nodes of Ranvier 
known as incisures of Schmidt. The axis cylinder of a nerve is merely a 
continuation of a ganglion cell, being made up of very fine fibrillae, with 
an intervening fluid substance. The white or medullary substance con- 
tains a large amount of fatty material, called myelin ( ). 
This sheath is supposed to act somewhat as an insulator. 

Nerve fibers and muscle fibers develop differently. The former are 
a composite structure formed of cellular elements which originate in 
various ways. For example, the nerve sheaths, though coming in contact 


General Biology 

with and surrounding the axis cylinder, have a totally different origin 
from the cylinder. It is interesting to know that in its development the 
axis cylinder is the first to make its appearance and comes from the 
exterior or ectodermic layer of the organism in which it develops, while 
the cells forming the sheath come from the mid or mesodermic layer. 

The negative manner of testing any of our scientific laws and prin- 
ciples may be illustrated here by calling attention to the fact that much 
of our knowledge of the position of nerves in various parts of the body 
does not come from our ability actually to trace them throughout their 
entire course, but by tracing the dying portion of an injured nerve. 
Having found that the cell is the important part of a nerve, and that 
whenever a fiber is cut between its cell and the termination of its 

— Node of Ranvter 
— Neurilemma 

Fig. 42. — Neurons of Various Types from Higher Animals. 

A, a complex of neurons from the cerebrum; B and C, neurons from the 
cerebellum; D, a single neuron from the cerebrum. E, diagram of a neuron or 
nerve unit. 

processes, it is that part still attached to the cell which will grow again, 
experimenters have cut nerve fibers and then watched that portion no 
longer connected with the cell proper, degenerate. By watching this 
and then observing those parts of the body which degenerate along 
with the dying nerve fiber, it is easy to see where the fibers actually 
pass and terminate. 

Nerve centers is the name given to those parts where several nerve 
cells are grouped together such as in the brain, spinal cord, ganglia, and 
the various ganglionic masses of the sympathetic system. The centers 
themselves consist of ganglion cells and their fibers, together with the 
connective tissue which holds them together, and the little vessels which 
supply them with nutriment and carry away waste products. 

Ganglion cells are usually quite irregular in outline with a single 

Histology of the Frog 117 

nucleus near the center. The cytoplasm is rather granular and, with 
certain stains, shows a network of tiny fibers connected directly with 
the fibrillae of the nerve fiber as well as with other processes of the 
cell. There are several kinds of processes. The axis cylinder process, 
already mentioned, requires a sheath and becomes part of a nerve fiber, 
and the protoplasmic processes, sometimes several in number, are shorter 
than the axis cylinder and usually branched. 

The cells themselves are designated as unipolar, bipolar, or multi- 
polar, in accordance with the number of processes they may give forth. 
Unipolar ganglion cells are found in the sympathetic ganglia. 




T has now been seen that the frog is a cold-blooded animal, an am- 
phibian, and a vertebrate. 

Its external features have been observed. 

Its internal structure, consisting of a series of organs known as 
systems, have been studied. These were : 

(a) The Digestive System. 

(b) The Circulatory System. 

(c) The Respiratory System. 

(d) The Excretory System. 

Concerned with Metabolism. 

(e) The Nervous System. T Concerned with regulation 

(f) The Endocrine secretions. J and control. 

(g) The Muscular System. Y~, , . a1 1 

)i \ -ri 01 1 j. 1 c> i [Concerned with locomotion, 

(h) The Skeletal System. r , 

; .( ^, T 1 \ support and protection. 

(1) I he Integumentary System.^ 

(j) The Reproductive System. Concerned with the propaga- 
tion of the race. 

It has been learned that organs are composed of tissues, and tissues 
in turn, of sheets of similar functioning cells. 

There were four general types of tissues : 

(a) Epithelial. 

(b) Connective. 

(c) Muscular. 

(d) Nervous. 

Tissues may also be classified according to their functional and 
structural character. For example, according to function, the epithelium 
is grouped as follows : 

(a) Glandular, which consists of secreting cells. 

(b) Sensory, which consists of sensory nerve cells and their 


(c) Germinal, which consists of those cells having especial 

growth or reproductive ability. 

(d) Protective, which goes to make up an outer covering of 

an organ or of the body itself. 

Summary of the Frog 


According to the structure of the composing cells, epithelial tissue 
is known as : 

(a) Cuboidal, 

(b) Cylindrical, 

(c) Columnar, 

(d) Squamos, 

(e) Stratified. 

Connective Tissue is known as : 

(a) Cellular, when it is composed almost entirely of cells with 

little substance in between them. 

(b) Homogeneous, if the entire substance looks very much 


(c) Fibrous, 

(d) Cartilage, 

(e) Bone. 

The Muscular Tissue is divided into : 

(a) Striated or Voluntary Muscles, 

(b) Non-striated or Involuntary Muscles, 

(c) Heart Muscle. 

The Nervous Tissue consists of cells known as : 

(a) Unipolar, 

(b) Bipolar, 

(c) Multipolar. 

Some writers call blood and lymph cells (Fig. 43) a fifth type of 

Red Corpuscles (ery- 
throcytes) ( " ) (caus- 
ing the characteristic red color 
of the blood) occur almost 
only in vertebrates. (In in- 
vertebrates, such as the earth- 
worm, the blood-plasma is 
red.) The red corpuscle has 
no nucleus in the mammal 
while in other vertebrates it 

White Corpuscles (leu- 
cocytes) ( ) are wan- 
dering cells in the blood and 
lymph, which are phagocytic 
( ) in their action, 
that is, they assist in keeping 
the body in health by devour- 
ing foreign substances. 

Fig. 43. . 

A, Red blood corpuscles (haematids) of the 
frog, stained with safranin and much magni- 
fied, to show the nucleus and nuclear net- 
work, bl, an amoeboid coarsely granular 
leucocyte from the frog's blood, showing trifid 
nucleus; b2, hi, b4, other forms of leucocyte 
from the frog's blood. c, discoid non- 
nucleated haematids from human blood, much 
magnified; cl, c2, c3, different forms of leu- 
cocytes from human blood. (After Bourne.) 

120 General Biology 

The various organs of the body are responsible for the particular 
size, shape, and function of the animal possessing them. 

There are two ways of looking at an organ : 

(a) Morphologically, or according to its structure or anatomy. 

(b) Physiologically, according to the function such organ 
may perform. 

If organs of different animals are physiologically equivalent, that 
is, if they function similarly, they are known as analogous organs. 

If the organs of different animals are morphologically equivalent, 
that is, if they have developed in a similar manner in relation to the 
other structures immediately surrounding them, they are called homolo- 
gous organs. 

There are three possibilities in comparing animals : 

(a) The organs may at the same time be homologous and 

(b) They may be homologous but not analogous, as for exam- 
ple the swim-bladder of fishes and lungs of mammals. 

(c) They may be analogous but not homologous, as for exam- 
ple the gills of fishes and the lungs of mammals. 

The functions of organs are said to be : 

(a) Vegetative (as in plants), when they have to do principally 
with growth. 

(b) Animal, referring to those functions which are absent in 
plants or but very slightly developed. In the animal kingdom they are 
considerably increased or are totally separate and distinct from any- 
thing the vegetable world may possess. 

The vegetative functions are equally complete in both man and the 
lower animals although they may develop quite differently in the two 

Animal functions are those of motion and sensation. The work of 
the various specialized sense organs, such as the eye and ear, come under 
this grouping, while the work of those organs which pertain to nutrition 
and reproduction, which both plants and animals possess equally well, 
are vegetative. 

Living matter has been shown to have four distinguishing charac- 
teristics : 

(a) Irritability, 

(b) Growth by intussusception, 

(c) Reproduction, 

(d) Nutrition. 

When nutrition is discussed biologically, it must be thought of in 
its widest sense as including not only the taking in of food and drink, 

Summary of the Frog 121 

and the digestive process consisting largely of fermentation and the 
absorption of such digested food, but also as including the taking in 
of oxygen through the respiratory tract to cause heat and energy, and 
the distribution through the circulatory system of the blood. And 
finally, there must be included the excretory system which eliminates 
all that for which the body has no further use. 

An organism was defined as any living thing capable of leading an 
independent existence. 

The frog is one of the higher organisms made up of organs, which 
in turn are made up of tissues consisting of sheets of similar functioning 

In the frog each group of tissues has a definite work to perform ; 
i. e., the eye only sees and the ear only hears, the bones only support, 
and the heart only pumps blood. 

This specialization in the work of an organ is known as a division 
of labor. 

There are hundreds of thousands of animals so small that they can- 
not be seen with the naked eye, many of which are composed of only 
a single cell. 

As they have only one cell they can have no tissues and consequently 
no organs. But, if they are living things,, they must possess the four 
characteristics which distinguish living matter. 

They do have these four distinguishing characteristics. Conse- 
quently the single-celled animal is as truly a living organism as is the 

But, as there are no organs and no tissues, the protoplasm in this 
single cell must be able to do all the different kinds of work which are 
done by the different organs in the frog. 

Therefore, in one sense of the word, the single-celled animal which 
is able to do all that a many-celled animal can do without any of that 
many-celled animal's organs, is much more complex and remarkable 
than is the so-called higher form. 

And lastly, even those organisms, highest in the scale of life, begin 
that life with a single cell which in turn grows by a division of that 
cell into two, then these two become four, these four eight, and so on 
until complete adultship is reached. 

With this summary in mind we may take up the study of the single- 
celled organisms. 



JUST as the frog is easily obtainable and most frequently studied in 
the laboratory, so the Amoeba (Fig. 44), because it may be found 
anywhere, is one of the classic forms of uni-cellular life that is made 
use of in the laboratory. This single-celled animal has the four char- 
acteristics necessary for a liv- 
ing being. It is found almost 
anywhere, but not necessarily 
everywhere. In fact, unless 
particular arrangements are 
made to have the Amoebae 
ready at the time they are 
wished for study, the probabil- 
ities are that they will not be 
found where one is looking for 

Just as with the frog, so 
with a single-celled animal, we 
attempt first to study its 
anatomy or morphology. We 
want to ascertain what seeable 
parts go to make up this tiny 
animal. We find in it all the 
constituents of a cell and all 
the needed characteristics to make an organism. 

There is an outer colorless layer of clear cytoplasm, called the ecto- 
sarc ( ), then a large central mass of grandular cyto- 

plasm, known as the endosarc ( ). A contractile 

or pulsating vacuole will usually be found lying in that part of the 
animal opposite the part which is moved most frequently. There may 
be several food vacuoles, various foreign substances such as grains of 
sand, and undigested particles (these latter depending, of course, upon 
whether the animal is studied immediately after it has been feeding 
extensively). Then there is also some material which has been digested 
and is ready for excretion, and a nucleus. The nucleus is not easily dis- 
tinguishable in living Amoebae. For this purpose animals are killed and 
stained, mounted upon slides, and studied very carefully with the com- 
pound microscope. 


Fig. 44. Amoeba Proteus. 

A, the animal in its natural condition; B, an ani- 
mal that has ingested a long filamentous plant; C, 
the animal in the state of division. 
cv, contractile vacuole; 
ec, ectosarc; 
en, endosarc; 

ex, remains of undigested food; 
p, protoplasm. (After Conn.) 

The Protozoa 123 

The nucleus changes with the various movements of the animal, so 
that it will not be found in the same location in all Amoebae. It has a 
rather firm nuclear wall, or membrane, and quite a number of spherical 
particles of chromatin are scattered about in the nuclear sap. The con- 
tractile vacuole usually lies near the nucleus, but as the vacuole grows it 
becomes further and further separated from the latter, and by the time 
it is ready to contract and expel its contents, lies close to the end farthest 
from the pseudopodia, at what is commonly called the posterior end. 
It then reappears close to the point of its disappearance, being carried 
along by the streaming protoplasm back to a position near the nucleus, 
again passing through the same stages just described. 

The fluid content of the contractile vacuole is believed to contain 
urea. As this is the common excretory substance of animals, the vacuole 
is probably excretory in function. It is likely that it is also respiratory 
for, in all probability, C0 2 passes to the exterior of the body from the 
vacuole. Oxygen is taken in through the outer surface of the body. It 
is well to compare Amoeba's physiological functions with the respiration 
of a higher animal such as the frog. The food vacuoles come into exist- 
ence whenever food is taken into the organism, each vacuole seemingly 
acting as a temporary stomach. 


The ectosarc, also called ectoplasm, sends out finger-like projections 
into which the cytoplasm of the cell then flows. These outpushings are 
known as pseudopods ( ), or rhizopods ( ). 

Often several of these pseudopods are thrust out at one time, although 
usually the one which comes in contact with some object gains the 
mastery, all of the animal then moving forward so that the cytoplasm 
extends into the outpushing. 

Various theories have been advanced to account for Amoebae's 
movements (Fig. 45), as follows: 

1. The adherence theory. This merely means that, if a drop of 
water or any inorganic liquid is placed upon a flat surface, a part of it 
coming in contact with some other substance, the entire drop will gravi- 
tate toward the attached end. Many pseudopods extend out into the 
surrounding liquid, however, and do not come in contact with any other 
solid substance. While this theory might explain those pseudopods 
which do become attached, it does not explain those which are known 
as free and which do not come in contact with solid objects. 

2. The surface tension theory. This theory is also taken from 
physics and chemistry and supposes that various currents move forward 
or outward in the central axis and backward along the surface. Unfor- 
tunately for this theory, the currents in Amoebae do not run that way. 

3. The contractile theory. 1 This theory has had a varying history, 

*It should be noted that this theory, even if true, in reality explains nothing. It simply pushes 
the problem back one step farther. That is, if it should prove true that Amoebae contain a con- 
tractile substance by virtue of whose properties they move, it would then be necessary to explain 
contractility in the substance — whence the property came, and what its actual meaning may be. In 
other words, we are forced back to a consideration of the fundamental physiology of the cell. 


General Biology 

although apparently it holds the stage as well as any, and better than 
most theories at this particular moment. The current seems to start at 
the foremost part of the animal and extends backward. Jennings has 
shown that Amoeba verrucosa resembles an elastic sac rilled with fluid. 
By placing this animal in a substance such as soot, which he caused to 
surround one of them, it was 





i ' '■ 

c m 

'*. * * - 

shown that the streaming fol- 
lowed the ectosarc toward the 
forepart of the animal, and just 
as it got beneath the Amoeba, 
remained there until the ani- 
mal had moved over it, when 
it again moved upward at the 
posterior end. 

Dellinger has shown that 

whether on floor or ceiling, 

wherever Amoebae are found 

to move, there is a sort of 

creeping walk by which one or 

more outer parts of the animal 

are extended at random. When 

this projecting part comes in 

contact with a solid substance 

the most posterior attachment 

relinquishes its pseudopod. It 

is, therefore, assumed that 

there is a contractile substance 

within the animal. 

All the various experiments along this line have depended upon 

surface tension for their explanation. However, even if the animal 

moves in a similar manner to a drop of liquid that is not living, it does 

not follow that the same force in each case causes the movement. 

It is essential that all of the subject headings under which the frog 
was studied should also be borne in mind when the single-celled animals 
come in for investigation. For example, in regard to metabolism, the 
following subjects must be studied just as in a more complex organism: 
Ingestion, digestion, egestion, absorption, circulation, assimilation, dis- 
similation, secretion, excretion, and respiration. 

It can readily be understood that there must be some instinctive 
process by which Amoebae know what food to ingest and what not to, 
or they might continue to take in sand particles and indigestible sub- 
stances which would cause the body to become so extended and heavy 
that the animal would die from this effect alone. There are, of course, 
no organs such as a mouth and intestinal tract, as in the frog. The 
food is taken in at any point of the body. This food consists of tiny 

Fig. 45. — Locomotion of Amoeba proteus. 

Photographs in side view. A and B show a speci- 
men attached at two points, a and b, and a pseudopod 
which projects from one end and bends down to the 
substratum as in B at d ; C shows the extension of a 
long pseudopod. (From Hegner after Dellinger.) 

The Protozoa 


aquatic plants, other single-celled animals, bacteria, and various types 
of animal and vegetable matter. 

It is of special interest to note that when food is taken by Amoeba 
the animal really places its body around the food (Fig. 46). Experi- 
ments with inorganic substances, such as a drop of chloroform in a 
watch glass of water, have shown that the chloroform will take in sub- 
stances like shellac, and paraffine and reject wood, glass, etc. It must 
not be forgotten, however, that these substances, which are thus accepted 
by the inorganic drop of liquid, are those which normally adhere to 
chloroform. But with Amoebae the majority of food substances do not 
adhere to the surface of the animal, and so again there is considerable 
dissimilarity between the experiment and the actual facts in the case. 
In digestion, the food vacuoles have been embedded in the 

endoplasm. The vacuole wall 
secretes a fluid containing some 
mineral acid, supposedly HC1. 
This digestive fluid seems to 
dissolve only proteid sub- 
stances, and has no effects upon 
fats and carbohydrates. Hofer 
performed an interesting ex- 
periment by cutting an Amoeba 
in two parts after it had just 
been well fed, and the part that 
did not have the nucleus was 
unable to digest food. 

A somewhat similar condi- 
tion will be found a little later 
in the study of the earthworm. If the earthworm is cut in two behind 
certain segments, the forepart of the animal, which contains the impor- 
tant organs, will regenerate a new tail, whereas the tail-part, which has 
been cut off, will regenerate another tail. Such an animal has no mouth 
and must consequently starve to death as it has no way of ingesting food. 
After digestion has taken place in Amoeba, any indigestible particle 
may be thrown out at almost any point on the surface of the animal. 
These indigestible substances are probably heavier than the protoplasm 
itself, so that this heavy portion sinks through the lower part of the 
animal's body. Then, as the animal moves away, it leaves the indi- 
gestible solid particle behind. 

There is no circulatory system proper in a one-celled animal, so that 
after the food has been digested, it must be absorbed and passed into 
the body substance proper of the animal. Here we come to a new term, 
that of assimilation, which means that now that new food matter has 
been digested and is within the body, there must be a rearrangement of 

Fig. 46. 

A, Amoeba encysted. 

B, Amoeba ingesting a plant, p, retracted pseudo- 
podium; dt, plant (diatom) taken in as food. cv, 
contractile vacuole; f.v., food vacuole; n, nucleus. 
(After Leidy and Howes.) 


General Biology 

some kind to form new particles and to add them to those already 
existing. It is this ability to manufacture protoplasm from unorganized 
matter that is one of the very fundamental properties of living matter. 

Any movement, or energy, expended by an animal is due to the 
breaking down of complex molecules by what is known as oxidation. 1 
The process of tearing down is called katabolism or dissimilation. This 
is a slow combustion process giving out heat and producing energy by 
which the animal can perform its various functions of life. The sub- 
stance thus broken down and "used up" must also be accounted for in 
any scientific study. This residual matter usually consists of solids and 
fluids ; namely, water and some mineral substance, urea and carbon 
dioxide (C0 2 ). Under this heading we include all secretions, excretions, 
and products of respiration. 

Whenever glands produce a substance which is to be used again 
by the animal, such product is called a secretion, while substances which 
are thrown out of the body entirely, are called excretions. 

The contractile vacuole, since it probably contains uric acid, is con- 
sidered an excretory organ, and because C0 2 also makes its way to the 
exterior of the organ, it is supposed to be respiratory likewise. Amoeba, 

like any animal, grows more rapidly than 
otherwise, if food is plentiful. Since food 
is taken internally, the growth comes from 
the center outward; in other words, by 

Whenever a cell reaches its full growth, 
its outer shell, membrane, or whatever its 
external covering may be called, not having 
infinite possibilities in the way of extension 
and stretching, usually breaks if more food 
is taken. Cell division is the process by 
which the plant or animal starts anew, thus 
saving the parent cell from breaking. A 
simple division into two (Fig. 47) is called 
binary division. It will be remembered that 
this mere splitting in two parts is the short- 
est method by which cells divide, but, which, 
as we have already said, probably does not 
occur at all. It is, therefore, only because 
our observational methods are not sufficiently delicate to note the 
exact processes, that we speak of amitotic division at all. In Amoeba 
proteus, however, which we are studying, there are two methods of 
division : The so-called simple binary or amitotic, just mentioned, and 
a process known as sporulation. A few instances have been reported 

Fig. 47. 

So-called amitotic division of 
Amoeba, showing the changes which 
take place during division. The 
dark body in each figure is the nu- 
cleus; the transparent circle, the 
contractile vacuole; the outer, clear 
portion of the body, the ectoplasm; 
the granular portion, the endo- 
plasm; the granular masses, food 
vacuoles. Much magnified. 

1 Oxidation may be likened to a series of infinitesimal explosions which could be detected if we 
had instruments delicate enough for such a purpose. 

The Protozoa 127 

where trie animal formed definite mitotic figures. Very few investigators 
have observed sporulation, but where it was observed the process lasted 
from two and one-half to three months. The pseudopodia were first 
drawn in, and the animal became spherical. A three-layered cyst was 
then secreted within which the Amoeba rotated for several days. Then 
all movement ceased. The nucleus divided until there were twenty or 
thirty nuclei present, all arranged near the surface. This division of 
nuclei continued until there were from five hundred to six hundred. 
Walls then appeared at the periphery, cutting off each nucleus with a 
small amount of cytoplasm. The wall of the cyst became soft and was 
broken to allow the small Amoeba to escape. Hundreds of these 
amoebulae, or pseudo-podiospores as they are sometimes called, broke 
out at one time to become recognizable as Amoeba proteus in from two 
and one-half to three weeks. No reason for such sporulation is known. 
Experiments have been made in which specimens were starved, given 
an excess of food, allowed to dessicate, or where they were transferred 
to water from different localities, but none of these experiments brought 
about encystment and sporulation. 

Whichever way the animal may divide it is simply a matter of 
growth before it is ready to divide again. We have here the interesting 
fact confronting us that these little single-celled animals are practically 
immortal. That is, they do not die. One may kill them by boiling and 
in other ways ; but, left to themselves, they will continue until they 
have reached their limit of adultship when they divide, each individual 
becoming two new and separate animals. 

It is important that the fact be grasped that in these little unicellular 
animals a parent does not give birth to its offspring. The parent itself 
becomes the offspring. That is, there are no ancestors. Each and every 
animal carries its complete and total ancestry with it. 1 


The way in which an animal reacts to a stimulus is called its 
behavior ; and when that behavior has not been learned, but comes forth 
without consciousness on the part of the animal, yet is protective to the 
animal, such behavior or reaction is called instinct. In these lower one- 
celled animals two words are used in discussing behavior and instincts. 
These are tropisms or taxis, 2 which merely mean a movement of some 
kind. To these words one adds the generic name of the stimulating 
cause, using the words positive and negative to explain one's meaning. 
For example, usually eight tropisms or taxis are mentioned : 

(1) Thigmotropism, meaning a reaction to contact of some kind; 

(2) Chemotropism, meaning a reaction to a chemical ; 

(3) Thermotropism, meaning a reaction to heat; 

1 An apparent exception to this statement arises if we accept, as a fact, that conjugation in the 
Infusoria is fundamentally a rejuvenation phenomenon as some biologists contend. Even if this be 
true, still there is nothing extra added, and the statement remains substantially correct. 

2 In a strict sense "tropisms" mean the growing or bending of an organism, or parts of an 
organism, in relation to external agents, while "taxis" refer to the active migration of organisms or 
cells. However, most modern writers are inclined to use these terms interchangeably. 


General Biology 

(4) Phototropism, meaning a reaction to light; 

(5) Electrotropism, meaning a reaction to an electric current; 

(6) Geotropism, a reaction to gravity; 

(7) Chromotropism, a reaction to color; 

(8) Rheotropism, a reaction to current. 

Amoebae move away from strong light, so that they are said to be 
negatively phototropic. They are also negatively thigmotropic. 

If an action is self-imposed, it is said to be autogenous 
( ) ; if an external object causes a reaction, whether 

such object be located within or without the body, the action is known 
as etiogenous ( ). 


This little organism (Fig. 48) moves about like a full-fledged ani- 
mal although it has chlorophyl in its body and manufactures its food 

as does the plant; and it does this notwith- 
standing the fact that it has a mouth and 

Euglena belongs to the Class Mas- 
tigophora ( ), which 

means that there is a whip-like flagellum 
protruding from its anterior end. Several 
animals must be grouped together in order 
that the naked eye may see any organisms 
present. When there are many in one place 
a characteristic green color is given the sur- 
rounding water. 


Euglena viridis is a single celled, 
elongated animal pointed at the posterior, 
and blunt at the anterior end. As in 
Amoeba, there are two layers in the cyto- 
plasm, the ectosarc, a dense outer layer, and 
the endosarc, a more fluid central mass. 
There is a thin cuticle running in parallel 
thickenings around the body of the animal 
in an oblique direction so that it appears 

The mouth is a funnel-shaped depression lying a little to one side 
of the center of the anterior blunt end. The gullet is a continuation of 
this depression. It looks like a duct, and connects with a large spherical 

A. Euglena viridis; m, the so- 
called mouth; n, the nucleus; e, 
the stigma; r, reservoir; c.v., con- 
tractile vacuoles; _ chr, _ chromato- 
phors; am, pyrenoids with sheaths 
of paramylum. B, another speci- 
men, showing change of shape and 
diagonal striation of the cuticle. C 
and D, outlines to show various 
stages of contraction. E, a free 
swimming specimen undergoing 
longitudinal division. F and G, divi- 
sion of an encysted form. (A-D, 
after Bourne; E-G, after Stein.) 

The Protozoa 129 

vesicle, the reservoir, into which several minute contractile vacuoles 
discharge their contents. 

There is also a red dot, called an eye-spot or stigma, close to the 
reservoir, near the inner end of the gullet. It is made up of small 
granules of haematochrome ( ). Because the 

anterior end of the animal seems to be more sensitive to light than other 
parts, it is supposed that this red stigma functions somewhat as an eye. 
It has been suggested that this red haematochrome is not the sensitive 
part at all, but that the protoplasm immediately beneath it is sensitive. 
As haematochrome has many of the characteristics of pigment granules 
of the eyes of higher animals, it is likely that we meet here with a sort 
of beginning eye. 

There is a single nucleus a little posterior to the center of the body. 
It has a distinct membrane. On the inside of the nucleus there is a 
so-called nucleolus. However, as this latter functions as a division 
center, it is probably not a nucleolus. 

There are a number of oval discs called chromatophores ( ) 

suspended in the protoplasm. These contain chlorophyl. In Euglena 
we meet with our first example of photosynthesis ( ). 

A little later, when plant-life is studied, it will be noted that this is the 
accepted method among plants of manufacturing their food. Photo- 
synthesis means that the chlorophyl is able, in the presence of light, to 
break down the carbonic acid (C0 2 ), and set free the oxygen to unite 
the carbon with water, thus forming a substance allied to starch called 
paramylum ( ). If specimens are kept in good 

light continually, a large amount of paramylum will be stored up for 
future use. This is laid down around some granules of proteid substance 
near the center of the body. These granules are called pyrenoids 
( ). The pyrenoids and the chromatophores are 

permanent cell structures. They increase in number by division and not 
by the origin of new ones from other parts of the body. 


The animal moves by means of its flagellum, which appears as a 
single whip-like structure, although really it is composed of four separate 
fibrils wound together. This flagellum begins in the body proper and 
extends through the wall of the mouth depression. It is often as long 
as the animal itself. In addition to the assistance rendered the animal 
in locomotion by this appendage, the entire animal is elastic, contracting 
and expanding, so that the body looks much like a worm in movement. 


As already stated, Euglena is like a plant in that it possesses 
chlorophyl and manufactures its own food. When an animal manufac- 
tures its food in this way it is said to be holophytic ( ). 
But as Euglena can live in the dark, and chlorophyl does not permit 

130 General Biology 

the manufacture of food without light, the animal must be able to feed 
also in some other way. When organic substance in solution is taken 
in through the body wall, as probably happens in the case of Euglena 
in the dark, such method of obtaining food is said to be saprophytic 
( ), while those animals which ingest solid particles 

of food like the frog are said to be holozoic ( ). 


Euglena, like Amoeba, when food becomes scarce, as well as for 
unknown reasons, may encyst. It does this by becoming spherical, 
secreting a rather thick gelatinous covering, and throwing off the 


This takes place by binary longitudinal division. The nucleus is 
divided by a primitive sort of mitosis. The body begins to divide at 
the anterior end. The old flagellum is retained by one-half of the body, 
while a new flagellum is developed by the other half. Division often 
takes place while the animals are in an encysted condition. One cyst 
usually produces two Euglenae, although these may divide while still 
within the old cyst wall so as to make four in all. Recent observers 
have recorded as many as thirty-one young, flagellated Euglenae which 
escaped from a single cyst. 


Euglena swims in a spiral manner as does Paramoecium. Like 
Paramoecium, too, it has only two reactions to the stimuli of touch. 
But in the case of Euglena, the forepart of the animal swings about in 
a circle while the posterior part remains more or less stationary, thus 
forming a sort of pivot around which the forepart moves. 

Euglena is positively phototropic, but direct sunlight will kill it. 
All plants and animals thrive in certain quantities of oxygen, moisture, 
and heat, but are injuriously affected if too much of these is applied. 
This explains phototropic action as well as the killing by an over- 
abundance of light. The environmental condition in which an organism 
thrives best, is called the optimum ( ) for such 



All unicellular animals which have whip-like flagella, come under a 
sub-grouping known as Mastigophora. This group is particularly inter- 
esting in that it furnishes us with our first example of unicellular animals 
forming colonies. The best known and studied of this group of colonial 
flagellata is Volvox (Fig. 49) found in fresh water ponds. Doflein 
found as many as 22,000 cells in a single colony. There is a division 
of labor in the colonies, for the various cells are not all alike, though 

The Protozoa 


each is a separate and distinct animal. Some of these cells are somatic 
and nutritive, while others are germ-cells or reproductive cells. Here 
we come in contact with the lowest form of sex life. Any organ which 
produces sex cells is known as a gonad. There are certain germ cells 
in a colony of Volvox called parthenogonadia ( ). 

These divide into many cells which drop into the center of the mother 

colony and finally escape through a 
break in the wall. There are other 
germ cells, however, which are also 
produced ; the smaller are called sper- 
matozoa or microgametes. These are 
the male germ cells, while the larger 
ones, called macrogametes or eggs, are 
the female germ cells. The eggs are 
fertilized by the spermatozoa, and, 
after passing through a resting stage, 
develop into new colonies. 

Colonies may be of one sex only. 
In such cases the male colonies can be 
recognized by the sperm pockets 
arranged in a wide belt around the 
middle of the colony with the poles 
free from cells. 

There is a distinct difference be- 
tween a colony of single-celled animals 
of this kind and a tissue. A tissue is a 
sheet of similar functioning cells, such sheet being combined with others 
to form an organ, 'while the organs, taken together, form a complete 
single individual. In Volvox there is no such grouping of sheets of 
similar functioning cells, Each cell is complete and distinct in itself 
and is as much an individual as Amoeba or Euglena just studied, except 
that it is attached to its fellows. 

Fig. 49. Volvox. 

The individual cells are united by radi- 
ating strands of protoplasm. A, a mature 
colony; a, spermaries; g, ovaries. B, zy- 
gote resulting from the fusion of the 
gametes. C, two sperm. D, egg. (From 
West, after Klein.) 


The malarial organism, Plasmodium malariae (Fig. 50), a member 
of the class Sporozoa, nearly all of which are parasitic, lives in the 
human body. Human blood contains minute circular disks, known as 
red blood corpuscles, within which the malarial organisms may be found 
in persons who are suffering from malaria, or chills and fever. The 
organism first appears as an extremely minute body, in shape somewhat 
like the Amoeba, though much smaller. It increases in size. After 
reaching a size which nearly fills up the red blood corpuscles, it breaks 
up into twelve to sixteen small spores. The blood corpuscles now break 
into pieces and the spores are liberated into the liquid blood. Each 


General Biology 

may then make its way into a corpuscle and repeat again the history 
just described. 

All of the following details of the life-cycle of Plasmodium malariae 
must be thoroughly understood and memorized by the student, because, 




/ J ^Penetration^ 
4 of red blood * 
j\^ cell by 
' f dporozoiies 


C2> O 

^ <*&> *^ 


M&rozdtes® 9 ® V© 

/"• \ 

gamei-sk : 

Phases Above Line Occur in Man ' ^^Jy 

<: y > 

Phases Mow Line Occur in Mosquito * 

% \ 




^y which 
I throws 
out the, 
j male^ 

Formation of 
capsule in 
stomach of mosquito C^okin ete^^^^]/J ^ Q 

Fig. 50. Life Cycle of Plasmodium Malariae. 

(1) Plasmodium malariae is the classic example of an animal-parasite 
of tremendous importance to man; (2) it is our best known example 
of a parasite which requires an intermediate host before being able to 
carry infection ; (3) it presents an excellent illustration of the methods 

The Protozoa 133 

used in obtaining experimental proof for scientific theories ; and (4) it 
brings home an understanding of the vast quantity of painstaking effort 
necessary to obtain that proof. 

The malarial organism, Plasmodium malariae, is a member of the 
class Sporozoa, nearly all of which are parasitic. It lives in the red 
corpuscles (therefore called Haematozoa) of human blood where it 
grows for a time, and then breaks up into from twelve to sixteen spores 
which rupture the corpuscle. The corpuscle itself then breaks up into 
tiny particles and the spores are thrown into the blood-stream. 

The malarial parasite has two life-cycles (Fig. 50), so to speak, one 
the sexual cycle, which develops in mosquitoes, and the other the asexual 
cycle, which develops in man. 

1. The sexual development of the malarial parasite within the body 
of the mosquito takes from eight to ten days. These sexual forms are 
known as gametes. 

The male cell (gamete) is also called a gametocyte. This gameto- 
cyte develops from four to eight microgametes which force their way 
into the large female cells (macrogametes). 

A sort of fertilization is thus set up. This fertilized cell is now 
called a migrating cell or ookinete. The ookinete penetrates the stom- 
ach-wall of a mosquito and builds a cyst (oocyst). Grassi says that 
there may be as many as five hundred oocysts at a time in the stomach- 
wall of a single mosquito. 

In the oocyst many tiny spherical bodies develop (sporulation). 
These spherical bodies are the sporoblasts (primitive spore-cells) which 
develop into thousands of sporozoites. These latter are merely tiny 
filaments which get into the lymph system of the entire body of the 
mosquito. As they reach the mouth-parts, they are ready to be injected 
into any human being which the mosquito bites. Once inside man, they 
enter the red-blood corpuscles and are known as schizonts (asexual 

From here on we must trace the asexual cycle of development in 
man. The injected organism which has been placed in the blood-stream 
of man is called a sporozoite. It finds its way into the red blood cor- 
puscles and becomes rounded and more or less ring-shaped, while it is 
amoeboid in movement. It is now a full-fledged schizont ( ). 

The schizont lives at the expense of the red corpuscle and deposits scat- 
tered black or reddish, so-called melanin granules. These granules 
should properly be called haematozoin granules ( ). 

The schizont now matures and becomes rosette-shaped when it is 
known as the morula. Its nucleus breaks into daughter nuclei, or 
rounded spores, known as merozoites ( ), the number 

of which may vary from six (in the Quartan fever parasite), to twenty 
(in the Tertian fever type). 

The red corpuscle is finally broken up. This liberates the merozoites 

134 General Biology 

into the blood-stream where (within an hour) they may again attack and 
enter other red blood cells. 

The breaking up of the red blood cells takes place at the moment 
the merozoite is mature, and the chills and fever likewise appear at this 

It will be readily understood that, when thousands of red corpuscles 
are thus removed from the circulation, the patient will be pale 
(anaemic). The chills may be due to the haematozoin granules, which 
possibly contain poisonous substances. 

This process of the merozoites being thrown out of the red cor- 
puscles into the blood stream may continue for some time, but after 
a while, rounded forms, which throw off tiny filaments, appear. These 
are the male sexual forms, while the larger macrogametes are the female 
forms. Both male and female forms, however, require a mosquito as 
host before being able to develop further. The sexual cycle, already 
described in the mosquito's body, now begins, if the infected individual 
is bitten by a female Anopheles mosquito. 

The chills always appear at regular intervals, because the incubation 
period of each of the three kinds of malarial parasites (although differing 
for each species) is always the same for the same species. Thus the 
tertian fever species (Plasmodium vivax) "hatches" every third day — 
hence its name ; the quartan (Plasmodium malariae) every fourth day 
while the aestivo-autumnal type (Plasmodium immaculatum Laverania) 
at irregular intervals. In fact, the physician uses this definite incubation 
period as his clue in diagnosing the case, to find what particular type 
of malarial parasite has infected his patient. . 

After the spores or merozoites are thrown into the blood-stream, 
many are devoured by the white corpuscles (leukocytes), but those not 
devoured, again enter new red corpuscles and so continue reinfecting 
the same patient, although they are unable to infect another. 

The method of communication from one person to another can only 
come about in the following manner: 

A female mosquito of the genus Anopheles must suck the blood 
of an infected person if the disease is to be communicated. As soon 
as the infected blood reaches the changed environment of the mosquito's 
stomach, the series of changes begins in the merozoites, which have been 
described above. It will thus be seen that Plasmodium malariae must 
not only pass through two stages of a life-cycle, sexual and asexual, but 
these two stages are unable to develop in a single host, the asexual stage 
developing in man, and the sexual in mosquitoes. 

At this point the question will occur, "How do we know all this?" 
It is the answer to this question which will give the student (1) the 
finest illustration of what modern laboratory methods mean ; (2) it will 
acquaint him with the exhaustive investigations which students of 
science are always performing, and (3) it will show him what great 

The Protozoa 135 

quantities of material must be sifted before one can prove an accepted 
scientific theory, or advance a new one. 

It was on November 6, 1880, that Dr. Laveran, a French army- 
surgeon serving in Algeria, plainly saw the living parasites under the 
microscope in the blood of a malarial patient. But it was not until five 
years later that medical men accepted his findings. Then several Italian 
pathologists, prominent among them being Golgi, Marchiafava, and Celli, 
worked out the behavior of the parasite in human blood. These men 
found that the fever and chills always came at definite periods of 
development in the parasite. 

But they could not find how the parasite got into the blood of the 
patient. The name "Malaria" is Italian and means "bad air" (malaria). 
As the disease had always been associated with swamps and stagnant 
water, it is not strange that mosquitoes had been thought of as having 
some relationship to the disease. Medical men were, however, inclined 
to consider such a thought as savoring too much of superstition to 
accept it. 

Notwithstanding this general attitude, Dr. A. F. A. King, an Amer- 
ican physician, in 1883 summed up the evidence which to him seemed 
quite conclusive for such an association. 

Riley and Johannsen have put Dr. King's argument in the following 
words : 

"1. Malaria, like mosquitoes, affects by preference low and moist 
localities, such as swamps, fens, jungles, marshes, etc. 

"2. Malaria is hardly ever developed at a lower temperature than 
sixty degrees Fahr., and such a temperature is necessary for the develop- 
ment of the mosquito. 

"3. Mosquitoes, like malaria, may both accumulate in and be ob- 
structed by forests lying in the course of winds blowing from malarious 

"4. By atmospheric currents malaria and mosquitoes are alike 
capable of being transported for considerable distances. 

"5. Malaria may be developed in previously healthy places by 
turning up the soil, as in making excavations for the foundation of 
houses, tracks for railroads, and beds for canals, because these operations 
afford breeding places for mosquitoes. 

"6. In proportion as countries, previously malarious, are cleaned 
up and thickly settled, periodical fevers disappear, because swamps and 
pools are drained so that the mosquito cannot readily find a place suitable 
to deposit her eggs. 

"7. Malaria is most dangerous when the sun is down and the 
danger of exposure after sunset is greatly increased by the person 
exposed sleeping in the night air. Both facts are readily explicable by 
the mosquito malaria theory. 

"8. In malarial districts the use of fire, both indoors and to those 

136 General Biology 

who sleep out, affords a comparative security against malaria, because 
of the destruction of mosquitoes. 

"9. It is claimed that the air of cities in some way renders the 
poison innocuous, for, though a malarial disease may be raging outside, 
it does not penetrate far into the interior (of cities). We may easily 
conceive that mosquitoes, while invading cities during their nocturnal 
pilgrimages, will be so far arrested by walls and houses, as well as 
attracted by lights in the suburbs, that many of them will in this way 
be prevented from penetrating far into the interior. 

"10. Malarial diseases and likewise mosquitoes are most prevalent 
toward the latter part of the summer and in the autumn. 

"11. Various writers have maintained that malaria is arrested by 
canvas curtains, gauze veils and mosquito nets, and have recommended 
the use of mosquito curtains, through which malaria can seldom or never 
pass. It can hardly be conceived that these intercept marsh-air but 
they certainly do protect from mosquitoes. 

"12. Malaria spares no age, but it affects infants much less fre- 
quently than adults, because young infants are usually carefully housed 
and protected from mosquito inoculation." 

King's work does not seem to have come under the notice of the 
European and Asiatic workers, so it was not until 1894 that Sir Patrick 
Manson, who had done pioneer work in filariasis (See Chapter XX), 
came to the conclusion that there must be an intermediate host for a 
parasite so similar in its general functioning as malaria is to filaria. 

It was already known that long thread-like processes formed as 
soon as the parasite escaped from the blood, and became free-swimming 
in the surrounding media. 

At first it was thought that water containing the parasite was the 
carrier of infection, but no persons who drank the water developed 
malaria; in fact, they did not even develop the disease when this water 
was actually injected into the veins. 

Manson then suggested that these motile forms must have some- 
thing to do with the manner of communicating the disease, and it was 
he who als'o thought a blood-sucking insect the most likely intermediate 
host. After so much progress had been made, it was a simple matter 
to think of the old association of mosquitoes and malaria. 

It is interesting to note also, that Laveran working independently, 
came to similar conclusions in the same year that Manson did. 

Major Ronald Ross, in India, without any knowledge of the form 
or appearance of the parasite during the time it is developing within 
its intermediate host, and without a knowledge of the species of the 
insect he was looking for, spent two and a half years of intensely 
arduous work following out experiments largely suggested by Manson. 

Finally, in August, 1897, seventeen years after the parasite was 
first discovered in man, he obtained his first clue. 

While he was dissecting a "dappled-winged" mosquito and had 

The Protozoa 137 

searched every cell and found nothing, he came to the insect's stomach. 
In writing of this, Major Ross says: "Here, however, just as I was 
about to abandon the examination, I saw a very delicate circular cell, 
apparently lying among the ordinary cells of the organ and scarcely 
distinguishable from them. On looking further, another and another 
similar object presented itself. I now focused the lens carefully on one 
of these, and found that it contained a few minute granules of some 
black substance, exactly like the pigment of the parasite of malaria. I 
counted altogether twelve of these cells in the insect." 

As he searched further he found that the mature pigment cells 
contained multitudes of thread-like bodies which, when the parent cell 
was ruptured, poured into the body of the insect. These were the spores 
formed in the sexual generation. 

Major Ross did his experimental work on birds which are infected 
with malaria, but his results were soon found to apply to man as well. 

So complicated a scheme of things can never appeal to men at large, 
and yet it is just men at large who must assist in any preventive meas- 
ures which are to wipe out diseases of this nature. For this reason a 
series of popular experiments was made. 

Drs. Sambon and Low, of the London School of Tropical Medicine, 
went to the most malarial portion of Rome in the most dangerous season. 
They lived with three or four others from July until the 19th of October 
in a specially constructed mosquito-proof hut near Ostia. They were 
thus protected from sunset to sunrise from the bites of mosquitoes. 
Not one of them became infected, while mosquitoes sent from here to 
London were allowed to bite several people (Dr. Manson's own son being 
one of the subjects who volunteered for the experiment), all of whom 
came down with the diseases. 

Again, in Italy, railroad employees who were housed in mosquito- 
proof huts did not develop the disease while those not so housed did. 

Our own experiences in cleaning up the Panama Canal Zone of 
malaria and yellow fever are notable examples of preventive measures 
used most effectively, from the knowledge gained in the study of the 
life-cycle of the malarial parasite. 

In Cuba, yellow fever (also a disease caused by an infecting parasite 
carried by the mosquito), was shown, likewise, to be carried only 
through an intermediate host. Major Walter Reed had workmen sleep 
in beds and use the clothing of those who died of yellow fever, but kept 
such men housed in mosquito-proof huts. Not one developed the disease, 
while those who were bitten by the infecting mosquito and having 
perfectly clean bedding and linen took the disease. Dr. Charles J. Finlay 
of Havana, Cuba, and Major Walter Reed are the Manson and Ross of 
the yellow-fever parasite. 

There are 125 species of mosquitoes in North America, but it is 
only the female of the genus Anopheles which can transmit malaria to 


General Biology 

man, though some members of the genus Culex do transmit it to birds. 
(At least this is true in India.) 

The distinguishing characteristics of the two groups is as follows 
(Fig. 51) : In Culex the wings are clear, while in Anopheles they have 

Fig. 51. 

A. — Life history of house mosquito (Culex). 

B. — Life history of malaria mosquito (Ano- 
pheles). (From Howard, U. S. Dept. of Agri- 

C. — Culex larva, showing details of external 
structure. (After Riley and Johannsen.) 

brown spots. In Culex the axis of the body forms a curved line as 
though the insect were hump-backed, while Anopheles presents a 
straight line when resting. For those familiar with insect anatomy we 
may add that Culex has short maxillary palpi while Anopheles has them 
almost as long as its proboscis ; and lastly, for those with a musical ear, 
we may add that the female Anopheles, which is the only one which 
carries the malarial parasite, sings several tones lower than the Culex. 

The eggs of Culex are always laid in a mass, while those of 
Anopheles are laid singly. As the eggs hatch, the larvae of Culex hang 
from the surface of the water at about an angle of 45 degrees, while the 
larvae of Anopheles lie almost parallel to the surface of the water. 

Prevention is always the scientific method of overcoming disease. 
Because mosquitoes lay their eggs in quiet pools, men conceived the 
idea of preventing these eggs from hatching. Such prevention of hatch- 
ing has not been possible, but oil poured on the water kills the little 
wrigglers after they have hatched. 

The breathing tubes of wrigglers are provided at their openings 
with hydrofuge plates which will not permit water to enter. Since these 
hydrofuge surfaces are due to the presence of oil, it is obvious that oil 
poured on the surface of the water will mix with this and cause the 
entry of oil into the breathing tubes, thus asphyxiating the wrigglers. 
It has been thought that certain kinds of fish destroy eggs and wrigglers. 

The Protozoa 


Muttkowski examined over 6,000 fish stomachs and found only one 
mosquito wriggler. Another observer examined about 2,000 specimens 
of gambusia, the so-called "mosquito-destroying top minnow," and found 
mosquito wrigglers in only about two per cent of the fish. 


The animal now to be studied is the Paramoecium (Fig. 52), a 
member of the class Infusoria. 1 Paramoecia are often called slipper 

animalculae because they are shaped 
like a slipper, or more correctly like 
a cigar. The distinctive characteristic 
of this animal is that its entire body 
is covered with little hair-like projec- 
tions, called cilia. The rapid move- 
ment back and forth of these cilia 
(especially those of the oral groove 
which beat faster than those on other 
parts of the body), causes the animal 
to be propelled through water. An 
oral groove extends obliquely back- 
ward from the forward end and 
empties just a little behind the middle 
Sfff?*^ portion of the body. The mouth is 
situated at the end of the oral groove, 
so that as the animal swims and con- 
stantly revolves, various substances 
are forced down this groove, and, as 
they reach the end of the groove, are 
thrust into the mouth proper. It also 
has an endosarc and ectosarc like in 
Amoeba, and an additional membrane 
or pellicle, sometimes called the 
cuticle. This is demonstrated by placing a drop or two of 35 per cent 
alcohol in a drop of water where some of the Paramoecia are found. The 
pellicle will raise like a blister, showing that this part is separate and 
distinct from the rest of the animal. Immediately beneath the cuticle 
is a layer of spindle-shaped cavities in the ectoplasm. These cavities are 
filled with a semifluid substance. They are known as trichocysts 
( ), supposed to be weapons of offense and defense 

(Fig. 53). If a little acetic acid, or ordinary blue or green fountain-pen 
ink, is added to the water, these trichocysts explode, and the long threads 
which they contain are discharged. 

There are two contractile vacuoles, one close to each end of the 

■Ant&rwr End 

■Food Vacuole/ 
■Food Particl&s 



Contractile Vacuole, Anterior 

Food Vacuole/ 
Oral Groove; 
Food Vacuole; 


Food Vacuole 
Food Parhcks 
Vhdig&si&d Food 
ntractile> Vacuole posterior 


7 ood Vacuole/ 
■Food Particles 

Posterior End 

52. Paramoecium caudatum. 
(After Biitschli.) 

1 The early workers in biology took vegetable matter, such ar, dried grass, steeped it in boiling 
water, and then left this infusion stand in the air. The animals found therein were called Infusoria. 

140 General Biology 

body, while six to ten radiating canals communicate with these vacuoles 
and other portions of the body. These canals collect the fluid from the 
surrounding protoplasm and pour it into the vacuoles, after which the 
vacuoles contract alternatively at intervals of about twenty seconds at 
ordinary temperature and discharge their contents to the outside of the 

This is as it is in Amoeba, where the contractile vacuoles act as 
organs of both excretion and respiration. Paramoecia feed on bacteria 
and certain other types of unicellular organisms. The 
animal moves back and forth rapidly, causing a cur- 
rent of water to be sent down the gullet so that 
various food particles are swept in. Along the gullet 
is a row of cilia, fused together, forming what is called 
an undulating membrane. As the food enters the end 
of the gullet, a food vacuole is produced, which, as 
soon as fully formed, separates from the gullet and is 
swept away by the rotary streaming movement of the 
fending itself from an endoplasm. This process is known as cyclosis 
?£? D%,uL Fr Tt ( .)• The digestion occurs within 

tnochysts are dis- the food vacuole, while the undigested particles are 

charged and mecban- . P *■ 

icaiiy force the ene- cast out at a definite anal spot which can only be seen 
SegnerTTfter Mast!) when these particles are discharged. 


Conjugation and division of Paramoecia will be discussed in the 
following chapter. Here only the ordinary reactions of this animal will 
be taken up. 

While Paramoecia normally swim by means of cilia, they can, when 
forced to, exhibit great elasticity and pass through very small openings. 
The body goes forward, turning round and round on its long axis, 
always toward the left as it is propelled forward. This results from the 
fact that the cilia in the oral groove grow more rapidly and effectively 
than elsewhere. Approximately the same effect is obtained as rowing 
in a boat in which the oars on one side are applied much more strongly 
than on the other. The animal would naturally swim in a circle if this 
were the only force applied, but as it rotates on its long axis continu- 
ally, it goes forward. This produces a spiral course. The swerving, 
when the oral side is to the left, is to the right, and when the oral side is 
above, the body swerves downward. When the oral side is to the right, 
the body swerves to the left, etc. The swerving in any given direction 
is, therefore, compensated by an equal swerving in the opposite direction. 
The resultant is a spiral path having a straight axis. 

Paramoecium responds to stimuli negatively and positively just as 
do other forms of unicellular animals. This animal has been particu- 
larly well studied in the laboratory as to its reactions to various stimuli, 
and it is interesting to note that whenever any injurious substance 01 

The Protozoa 141 

stimulus is applied at its anterior end, the cilia reverse themselves and 
the animal swims backward for a short distance away from the object 
or substance causing stimulation. The forepart of the animal then 
swings about, using the posterior part as a pivot, and the animal again 
moves forward. If it again comes into an undesirable medium, the 
same process is repeated. As the animal backs up from an unpleasant 
stimulus, using its posterior end as the pivot upon which to turn, various 
samples of the surrounding medium are brought into the oral groove, 
so that, as soon as these samples of liquid no longer contain the unpleas- 
ant stimulus, the animal moves forward. 

The important point to remember here is that Paramoecium has 
only two reactions, the going forward and the going backward. 1 Much 
erroneous interpretation may be avoided if this be remembered when 
the study of the animal mind, or animal psychology, is taken up later; 
for, no matter how many hundreds of times an animal of this kind may 
make an experiment, it always continues this trial-and- error method of 
going forward, bumping into something that is antagonistic to itself, 
backing up, and again coming forward until it accidentally gets into a 
medium that is satisfactory. In fact, there are some substances, such 
as acetic acid, to which Paramoecia react in a peculiar manner. If a 
drop of this acid be placed before the animal, it will enter the liquid ; 
but once within the acid-drop it will react to the surrounding water 
in a negative manner ; that is, it will come to the edge of the acid-drop 
and then back away again and again. Then, the trial-and-error method 
may be observed when heat is applied to the surrounding media. The 
animal tries almost every direction until it finds some method of escaping 
from the unfavorable stimulation. The optimum temperature is nor- 
mally between 24° and 28° C. 

There are positive reactions of Paramoecium also, such for example 
as its habit of lying against solid objects. Paramoecia are negatively 
geotropic, in that they usually come toward the upper portion of the 
water in which they are placed. The animals usually swim upstream, 
and it is supposed that the reason for this is that the current might 
interfere with the beating of the cilia if another direction were taken. 

It is generally supposed that it is the physiological condition of 
Paramoecium which determines the character of any response to a given 
stimulus. This means merely that the actions are more or less spon- 
taneous and due to the internal condition of the animal (autogenous). 
This internal condition changes, however, with the different amounts 
and qualities of food and digestion. One physiological state really 
resolves itself into another. This "becomes easier and more rapid after 
it has taken place a number of times," giving ground for the belief that 
stimuli and reaction have a distinct effect upon succeeding responses. 

x These two reactions are, of course, in addition to the animal's regular revolving method of 


General Biology 

One writer has summed up the external factors that produce or 
determine reactions as follows : 

"1. The organisms may react to a change even though neither 
beneficial nor injurious. 

"2. Anything that tends to interfere .with the normal current of 
life activities produces reactions of a certain sort (negative). 

"3. Any change that tends to restore or save the normal life 
processes may produce reactions of a different sort (positive). 

"4. Changes that in themselves neither interfere with nor assist the 
normal stream of life processes may produce negative or positive re- 
actions, according as they are usually followed by changes that are 
injurious or beneficial. 

"5. Whether a given change shall produce a reaction or not often 
depends upon the completeness or incompleteness of the performance 
of the metabolic processes of the organism under the existing conditions. 
This makes trie behavior fundamentally regulatory." 

When one organism causes disease in another, it is said to be 
pathogenic to the organism affected. For example, Amoebae bucallis 
are found in pyorrhea, a disease of the teeth. The drug emetine kills 
Amoebae bucallis, and when these are killed, the diseased condition 
improves. From these facts it has been concluded that this particular 
protozoan is the cause of pyorrhea, although this is not strictly true. 

While, as we shall shortly see, most of the pathogenic organisms 
belong to the plant kingdom, still the following animal organisms which 
cause disease in man, are rather important factors in the study of 

Fig. 54. 

Entamoeba histolytica from a case of amoebic dysentery in man. Ectp., ecto- 
plasm; Endp., endoplasm; V, vacuoles; N, nucleus, cy, encysted amoebae. (After 

The Protozoa 


Class I. Rhizopoda. 

(a) Entamoeba hystolytica (also called entamoeba dysen- 
teriae), (Fig. 54). 

Entamoeba histolytica causes a chronic ulcerative process in 
the large intestine, the so-called amoebic dysentery. The organisms are 
frequently carried to the liver by the portal circulation and give rise to 
abscesses which may attain large size and may extend to a pleural cavity 
or to a lung. 

It is a common infection in the tropics, but occurs also more 
or less frequently in temperate zones. 

The organism measures fifteen to twenty-five micra in diam- 

Fig. 55. 

Entamoeba gingivalis (buccalis). (After A. T. Smith in Dental Cosmos, Sept., 

eter. It contains a small, round vesicular nucleus which stains but 
poorly with the ordinary basic dyes and with alum hematoxylin. The 
nucleus contains a minute nucleolus. The cytoplasm around the nucleus 
is finely granular and is surrounded by an outer zone or ectosarc which 
is transparent and refractive, and which sharply defines the outer limits 
of the organism. 

The entamoeba hystolytica must be examined on a warm stage 
in order to detect the characteristic movements ; but it is readily 
identified in properly fixed tissues owing to its characteristic morphology. 

The organism is quite phagocytic and is frequently found to 
contain red blood corpuscles, bacteria, or cellular debris. It is able to 
penetrate fibrous and other tissues and is frequently found in the walls 
of blood vessels as well as within the blood vessels themselves. 

It secretes a mild toxin (which may be a waste product). This 
secretion slowly kills the cells in its neighborhood and then gradually 
dissolves them. 

Amoebae are, however, often found in normal tissues. Some- 
times the nuclei seem to be fading out. 

The organisms are found principally in the intestines, but some- 
times also in the liver. 

Cultures of these amoebae have been shown to withstand drying 
from eleven to fifteen months. 

(b) Entamoeba buccallis (also called E. gingivalis and E. den- 


General Biology 

talis) has been said to cause pyorrhea alveolaris (Fig. 55), but Rivas 
holds that these Amoebae are the effect of infection and thus represent 
a secondary infection which aggravates the primary infection. 

Class II. Sporozoa. 

Subclass 1. Telosporidia ( ). 

Order 3. Haemosporidia ( ). 

Plasmodium, which causes malaria. (See Fig. 50.) 

Subclass 2. Neosporidia ( ). 

Order 2. Sarcosporidia ( ). 

Sarcocystis miescheriana. (Fig. 56.) 

Medical men often call these organisms "Rainey's tubes." They 
are found in the muscles of pigs. 

The tubes are ovoid bodies filled with small sickle-shaped 
unicellular organisms — the Sarcocystis miescheri. It sometimes is found 
in man, where it causes a serious disease called psorospermiasis, usually 

Class III. Mastigophora. 
Order 1. Flagellata. 
Trypanosoma gambiense (Fig. 57) causes the disease known 

Fig. 56. 

Longitudinal section 

through muscle of a Pig, 
c o n t a i ning Sarcocystis 
Miescheriana (From 

Kiihn, after Braun). 

Trypanosoma gambiense, from 
a case of sleeping sickness. 
Different forms. (After Man- 

as trypanosomiasis, commonly called sleeping sickness. 

This parasite is found in many invertebrates and vertebrates. 

Its life history is divided into two stages. One a flagellate 
monadine ( ) phase, in which the organisms live in the 

blood-stream of vertebrates, in some of which they cause serious disease ; 
the other is a gregarine ( ) non-flagellate phase which 

may also be parasitic. This latter type is met with in forms of Kala 

This organism causes sleeping sickness, which is common in 

The Protozoa 


West Africa. Those living on wooded shores of lakes and rivers, such 
as fishermen and canoe men, are subject to it. The parasite is carried 
by the bite of the tsetse fly (glossina palpalis). Wherever this insect 
is found the disease is likely to prevail. The fly lives on bushes on the 
shores of lakes or river banks, and feeds on the blood of crocodiles, 
antelopes, etc. The trypanosomes undergo various changes in the body 
of the fly. The infectivity does not appear until the thirty-second day, 
but continues for at least seventy-five days. 

The parasite is found mostly in the cerebro-spinal fluid and 
less commonly in the blood. Hope of exterminating the disease seems 
to lie in exterminating the game (crocodiles especially) on which the 
tsetse fly feeds. 


5 6 7 

Fig. 58. 
Kala-Azar organism. 1, from a patient in India; 2 and 3, individual flagellate, 
(Leishmania Jonovani) ; 4, 5, 6 and 7, Leishmania infantum. (From Kolle- 

Leishmania donovani. 
Leishmania infantum. 
Leishmania tropica. 

Causes Indian Kala Azar (dum-dum fever), Infantile Kala Azar, 
and tropical boil, respectively. Common in Asia. Causes lesions on 
exposed surfaces of body, enlargement of the spleen, and anaemia. 

The bed-bug or a blood-sucking bug is 
probably the common carrier because ingested para- 
sites undergoing development into flagellate forms 
have been found in the bed-bug. 

The infantile disease affects children only ; 
probably through dog fleas, as dogs are spon- 
taneously infected in the epidermic regions. 
Class IV. Infusoria. 

Balantidium coli (or Entamoeba coli). 
(Fig. 59.) 
Fig. 59. A ciliated, oval-shaped infusorian with a 

Balantidium coli, from i„„i_„j i j i • i 

an ulcer of man's intes- bean-shaped marco-nucleus and a spherical micro- 
Luhe.) (After Braun and nucleus. The organisms frequently exhibit changes 


General Biology 

in form due to ameboid motion, as for example, when they penetrate the 
epithelial lining of the intestinal glands. 

This parasite is a common inhabitant of the intestine of the 
hog but it causes no lesion there. On rare occasions it is apparently 
transferred to man where it gives rise to more or less extensive ulcera- 
tions in the large intestine (rarely in the lower end of the small intestine) 
accompanied by persistent diarrhea. The disease may terminate fatally. 

These parasites are also found in the lumen and walls of the 
intestine, but usually they penetrate the epithelial wall and lie next to a 
gland. Some collect in the lymph-nodules. Often they are found in 
lymph-vessels and veins, but they do not seem to be distributed by the 
streams of these vessels. They have likewise been found in the liver. 

They do not seem to produce a toxin but do a mechanical injury 
only, although this injury opens paths through which bacteria often 
cause infections. 

The ulcers caused by this organism resemble those caused by 
entamoeba histolytica. 

Fig. 60. 

A. Partially schematic drawing of Trichomonas intestinalis. 

B. Trichomonas muris dividing (5 stages). 

C. Lamblia intestinalis. a, flagellated form; b, cyst; c, flagellated form viewed 
from the side. 

D. Cercomonas hominis. a and b, show different forms of the organism; 
c, cyst. 

(From Kolle-Wassermann; B, after von Kuczynski; C, after Benson and 
Grassi and Schewiakoff; D, after Wenyon.) 

The Protozoa 



Trichomonas hominis (Fig. 60). 
Cercomonas hominis. 

In intestines, causing acute or chronic diarrhea. 
Lamblia intestinalis. 

Larger than the trichomonas. Flagellated forms have been 
found in the sputum of cases of gangrene of lung, and in those having 


Borrelia recurrentis (formerly Spirochaeta recurrentis). (Fig. 

61.) , 

Causes Relapsing Fever 

(also called Famine Fever, Seven 
Day Fever, and Tick Fever), prob- 
ably transmitted by mosquitoes or 
bugs. From five to seven relapses 
take place after all symptoms have 

The spirillum or spirochete 
is 15 to 40 micra long, shaped like 
a corkscrew. Quite motile and 
present in blood during the febrile 

paroxysms, disappearing at intervals. 

The disease has been reproduced by injecting into a healthy 

monkey the blood sucked by a bug from an infected animal. 


1. Borrelia recurrentis, found in Russia. 

2. Same as 1, but from a patient in Africa. 
(From Kolle-Wassermann.) 


e MW^ 


Fig. 62. 

Schematic drawing of undulating membrane of Spirochaetes. a and b Spiro- 
chaeta pallida; c, S. refringens ; d, a small Spirochaete of the same species; 
e, Spirochaete found in an ulcerated carcinoma; f, Spirochaete dentium; g, Spi- 
rochaeta plicatilis merely showing the extremity of a rather long individual. 
(After Schaudinn.) 

Treponema Pallidum (Fig. 62). 

Cause of syphilis. 

Acquired syphilis is due to a mucous membrane coming in 
contact with the spirochete. 

Congenital syphilis is transmitted through the mother to the 

The treponema is a spiral, curved organism from five to fifteen 
microns in length, showing active movements in fresh specimens. 

148 General Biology 

Syphilis is one of the most serious and far-reaching of all dis- 
eases, in fact so far-reaching that one of the world's greatest diagnos- 
ticians has said that, if one could know every ramification of this disease, 
he would know nearly all there was to medicine. It is doubtful whether 
the disease is curable. 

Though all symptoms are gone, the disease may appear again. 

In fact, in prisons, where there was little likelihood of a second 
infection, symptoms have appeared ten years after a supposed cure. 


(Table Modified from R. Hertwig and R. W. Hegner.) 

1. The Protozoa are unicellular organisms without true organs or 
true tissues. 

2. All vital processes are accomplished by the protoplasm (sar- 
code), digestion directly by its substance, locomotion and the taking of 
food by means of protoplasmic processes (pseudopodia), or by appen- 
dages (cilia and flagella). 

•3. Excretion takes place by special accumulation of fluid, the con- 
tractile vacuoles. 

4. Reproduction is by budding or by fission. Conjugation has 
been witnessed in many, and possibly occurs in all. True conjugation 
is a process of fertilization (caryogamy), in contrast to fusion of plasma 

5. Protozoa are aquatic, a few living in moist earth. They can 
only exist in dry air in the encysted condition, surrounded by a capsule 
which prevents desiccation. 

6. Since encysted Protozoa are easily carried by the wind, the 
occurrence of these animals in water which originally contained none is 
easily explained. 

7. The mode of locomotion serves largely as a basis for division 
of the Protozoa into the classes Rhizopoda, Mastigophora, Infusoria, 
and Sporozoa. 

8. The Rhizopoda are subdivided into the following orders : 
Lobosa, Heliozoa, Radiolaria, and Foraminifera. 

9. The Rhizopoda have changeable protoplasmic processes, the 

10. Order 1. Lobosa ( ). Rhizopoda with 
fingerlike (lobose) pseudopodia. Most of the Lobosa occur in fresh 
water, a few in moist earth, and some are parasites. 

Examples: Amoeba, Arcella and Difflugia. (Fig. 63 .) 

Arcella ( ) is common in the ooze on the bot- 

toms of fresh-water ponds and ditches. It has a dome-shaped brownish 
shell of chitin which it secretes. The lobose pseudopodia protrude from 
a circular opening in the center of the flattened surface. 

Difflugia ( ) is another common member of the 

order Lobosa, and is also found in the ooze of ponds. Its shell consists 

The Protozoa 


of minute particles of sand and other foreign objects held together by 

Fig. 63. 

A. Amoeba proteus. (After Gruber.) 

B. and C. Arcella discoides. (After Leidy.) 
D. Difflugia urceolata. (After Leidy.) 

11. Order 2. Heliozoa ( ) Rhizopoda with 

thin, radially arranged pseudopodia, which are usually supported by 
axial threads. 

Examples: Actinophrys. (Fig. 64.) 

Actinophrys ( ), the sun animalcule, lives 

among the aquatic plants in fresh-water ponds 
and ditches. The body appears vesicular, be- 
cause it is crowded with vacuoles. The small 
organisms which serve as food strike the 
pseudopodia, pass down to the body, and are 
engulfed ; larger organisms are drawn in by 
several neighboring pseudopodia acting to- 

12. Order 3. Radiolaria ( ) 

Marine Rhizopoda with raylike pseudopodia, a 
central perforated capsule of chitin, and usually 
a larger enclosing skeleton of silica. 
Examples: Actinomma, Thalassicola. (Fig. 65.) 
The shells of the radiolarians, upon sinking to the sea bottom, form 
radiolarian ooze. This becomes hardened, producing rock strata as much 
as 1,000 feet thick. These rocks may take the form of quartzites, flint, 
or chert concretions. 

13. Order 4. Foraminifera ( ) Rhizopoda, 

mostly marine, with fine, branching pseudopodia which fuse, forming a 
protoplasmic network. 

Examples: Allogromia, Globigerina. (Fig. 66.) 
Allogromia ( ) lives in fresh water and has a 

chitinous shell. The shells of many Foraminifera consist of numerous 

Fig. 64. 
Actinophrys sol 
(From Bronn.) 


General Biology 

chambers connected by openings (foramina), and are composed of cal- 
cium carbonate. When these shells sink to the sea bottom, they become 
Globigerina ooze, which solidifies, forming gray chalk. 

Fig. 65. 

A. to H. Isolated Nucleus of Thalassicola nucleata Hux. (After Verworn.) 

A. to D. Regenerative changes. 

E. to H. Degenerative changes. 

I. Actinomonas Pusilla (Kent) n, nucleus; /, flagellum; p, pseudopodia. 

14. The Mastigophora ( ) may easily be dis- 

tinguished from other Protozoa by the presence of one or more flagella. 
Four orders are usually recognized: (1) Flagellata, 
(2) Choanaflagellata, (3) Dinoflagellata, (4) Cysto- 

15. Order 1. Flagellata ( ) 

Mastigophora with one or more flagella at the an- 
terior end of the body. 

Examples : Euglena, Mastigamoeba, Chilomo- 
nas, Uroglena, Volvox. (Fig. 67.) 

Mastigamoeba ( ) is of 

Proto lasm 6 o'f Giobi s P ec i a l interest, since it appears to combine the dis- 
gerina, after the shell has tinguishing characteristics of both the Rhizopoda 

been dissolved. n, nu- , , , . , . M . . .. 

cieus. (After Hertwig.) and Mastigophora ; that is, it possesses pseudopodia 

Fig. 67. 

A. Uroglena americana, Calkins, a sphareoid colony. 

B. Mastigamoeba as per a. (After Schultze.) 


The Protozoa 


and also a distinct flagellum. It is, therefore, able to creep about on 
a solid object, or swim directly through the water. 

Chilomonas ( ' ) is a very common flagellate in 

laboratory cultures. Uroglena forms spheroidal colonies consisting of 
a great number of individuals held together by a gelatinous matrix. This 
form is often responsible for the "oily odor" of drinking water, caused 
by the escape of small droplets of an oily substance from the cells. 

Volvox ( ) (Fig. 49) is a colonial flagellate 

found in fresh-water ponds. It may'consist of as many as twelve thou- 
sand cells. Protoplasmic strands connect each cell with those that sur- 
round it ; physiological continuity is thus established. All of the cells 
are not alike, since some of them, the germ cells, are able to produce new 

Fig. 68. 

Proterospongia haeckeli S. K. 
(S. Kent.) 

Fig. 69. 

A. Peredinium divergens, chr. 

B. _ Ceratium tripos (Calkins). (From Pratt's "Manual" by 
permission of A. C. McClurg & Co.) 

colonies, while others, called somatic or body cells, have no reproductive 

Some of the germ cells, the parthenogondia ( ), 

grow large, divide into many cells, drop into the center of the mother 
colony, and finally escape through a break in the wall. Other germ 

Noctiluca millaris. A, entire animal; f, flagellum; n, nucleus; o, cytostome 
and beside it the tooth and lip; t, tentacle; B, C, upper end with two stages in 
the formation of zoospores; D, zoospores. (After Hertwig.) 


General Biology 

cells produce by division a great number of minute microgametes or 
spermatozoa, and still others grow large, becoming macrogametes or 
eggs. The eggs are fertilized by the spermatozoa, and, after a rest- 
ing stage, develop into new 

16. Order 2. Choano- 
flagellata ( ) 
Mastigophora with a con- 
tractile protoplasmic collar 
from the bottom of which 
extends a single flagellum. 

Examples : Monosiga, 
Proterospongia. (Fig. 68.) 

17. O r d e r 3. Dino- 
flagellata ( ) 
Mastigophora with two 
flagella, one at the anterior 
end, the other passing 
around the body, often in a 

Examples : Peridinium, 
Ceratium. (Fig. 69.) 

18. Order 4. Cystoflag- 
ellata ( ) 
Mastigophora with two 
flagella, one resembling a 
tentacle, the other lying in 
the gullet. 

Examples : Noctiluca, 
Leptodiscus. (Fig. 70.) 

Enormous numbers of 
Noctiluca ( ) 

are often found floating near 
the surface of the sea, giving 
it the appearance, as 
Haeckel says, of "tomato 
soup." At night they are 
phosphorescent, emitting a 
bluish or greenish light. 

19. The Sporozoa 
( ) are 
Protozoa without motile or- 
gans. They are parasitic in 
Metazoa. Reproduction is 

mainly by spore formation. The following classification is simplified 
from Minchin's account in Lankester's Treatise on Zoology, Part 1 : 

Fig. 71. 

Different Gregarina. I-VII, development of Stylor- 
hynchus; I, S. longicollis ; II, encysted S. oblongatus (two 
animals) beginning gamete formation; 777, same later 
when the sexually differentiated gametes are copulating; 
IV-VII, formation and development of zygote of S. 
longicollis more enlarged; IV, copulation of gametes; V, 
A, Clepsidrina blattarum. 1-4, Monocystis magna. 1, 
two individuals copulating while in the spermatheca of 
an earthworm, surrounded by spermatozoa; 2, encysted; 
3 and 4, parts of cysts, formation and conjugation of the 
more enlarged gametes. cu, cuticula; dm, deutomerite; 
ek, ectosarc; en, entosarc; g, gametes; gl, zoospores; 
g2, oospore; pm, protomerite; n, nucleus; r, residual 
body; s, sperm of earthworm; z, zygote. (From Hertwig 
after various authors.) 

The Protozoa 


Development of Coccidium schnbergi 1, entrance of sporozoites in cell; 2, its 
growth; 3, nuclear multiplication; 4, division into merozoites; 5, macro-and 
microgametes; 6, zygote divided into four sporozoites. 8-11, Emeria stiedae. 8, 
auto-infection; 9, formation of sporoblasts; 10, change of spores into sporozoites; 
11, spore with two sporozoites, much enlarged; c, z, sporozoite; e, epithelial cell; 
k, ii, nucleus; mi, microgamete; o, macrogamete; r, residual body; sp, spore; 
sp', sporoblasts. (1-7 after Schaudinn; 8-11 after Wasielewsky and Metzner.) 

20. Subclass 1. Telosporidia ( ) Sporozoa in 
which the life of the individual ends in spore formation. 

21. Order 1. Gregarinida ( ) Telosporidia 
possessing a firm pellicle and complex ectosarc ; intracellular during the 
early stages of the life cycle, later free in the body cavities of inverte- 

Examples: Monocystis, Porospora, Gregarina. (Fig. 71.) 





A. B. C. 

Fig. 73. Plasmodium malariae. 

A. Parasites of tertian malaria. 

B. Parasites of estivo-autumnal malaria. 

C. Parasites of quartan malaria. (After Thayer and Hewetson.) 
(From supplement No. IS to the Public Health Service, /an. 20, 1915.) 


General Biology 

Monocysts ( ) may be found in the seminal 

vesicles of almost every earth-worm ; Gregarina is a common parasite of 
the cockroach ; and Porospora gigantea, which reaches a length of two- 
thirds of an inch, inhabits the alimentary canal of the lobster. 

22. Order 2. Coccidiidea ( ) Telosporidia simple 
in structure ; trophozoite is a minute intracellular parasite. 

Example: Coccidium. (Fig. 72. ) 

Members of this order are sometimes found in the liver and intestine 
of man and other vertebrates, and in Arthropoda and Mollusca. 

23. Order 3. Haemosporidia ( ) Telosporidia 
parasitic in the blood of vertebrates. 

Example: Plasmodium. (Fig. 73.) 

24. Subclass 2. Neosporidia ( ) Sporozoa which 
give rise to spores at intervals during active life. 

25. Order 1. Myxosporidia 
( ) Neosporidia 
with ameboid intercellular tropho- 

Example: Nosema. (Fig. 74.) 
The Myxosporidia are parasitic 
especially in Arthropoda and fish, 
frequently causing serious epidemics 
in aquaria. Nosema bombycis pro- 
duces the silkworm disease, pebrine. 

26. O r d e r 2. Sarcosporidia 
( ) Neosporidia 
usually parasitic in the muscles of 

Example: Sarcocystis. (Fig. 75.) 
The most common Sarco- 
sporidia are Sarcocystis miescheriana 

in the muscle of the pig; S. muris, in that of the mouse; S. lindemanni, 

rarely occurring in the muscles of human beings. 

27. The Infusoria ( ) are protozoa with cilia 
which serve as locomotor organs and for procuring food. Paramoecium 
is a typical member of the class. There are two subclasses, (1) Ciliata, 
and (2) Suctoria. 

28. Subclass 1. Ciliata ( ) Infusoria with cilia 
in the adult stage, a mouth, and usually undulating membranes or cirri. 
Many ciliates are confined to fresh water, others occur either in fresh or 
salt water, and still others are parasitic in Metozoa. 

29. There are four orders: (1) Holotricha, (2) Heterotricha, (3) 
Hypotricha, (4) Petritricha. 

30. Order 1. Holotricha ( ) Ciliata with cilia 
all over the body and of approximately equal length and thickness. 

Nosema. Longitudinal section of stomach of 
honeybee showing infection with Nosema apis: 
ep, Epithelial portion, containing spores of the 
parasite stained black. (The younger para- 
sites, not differentiated so easily by staining, 
are not shown; they are found toward the base 
.of the cells reaching the basement membrane 
(bm), but do not extend beyond it. Younger 
spores sometimes show an unstained area at 
one end and occasionally at both ends. m, 
muscular portion of stomach wall showing an 
outer and an inner longitudinal muscular layer 
and a middle circular one. (After G. F. White, 
U. S. Dept. of Agriculture Bulletin No. 780.) 

The Protozoa 


Examples: Paramoecium, Coleps, Loxophyllum, Colpoda, Opalina. 
(Fig. 76.) 

The Holotricha are probably the most primitive Infusoria. Para- 
moecium caudatum is the best known species. Members of the follow- 
ing genera are frequently found in fresh-water cultures : Coleps, 
Loxophyllum, and Colpoda. Opalina ranarum is a large multi-nucleate 
species living in the intestine of the frog. It has no mouth, but absorbs 
digested foods through the surface. 


Fig. 75. Sarcocystis 
A, a cyst; B, Pork 
containing cysts. 
(From Pratt's ''Man- 
ual" by permission of 
A. C. McClurg & Co.) 

Fig. 76. 

A. Coleps hirtus Ehr. (After Maupas.) 

B. Division phase of A. 

C. Opalina ranarum. (After Bronn.) 

D. Colpidium colpoda. (Calkins.) 

E. Loxophyllum rostratum. (Conn.) 

31. Order 2. Heterotricha ( ) Ciliata whose 
cilia cover the entire body, but are larger and stronger about the mouth 
opening than elsewhere. This adoral ciliated spiral consists of rows of 
cilia fused into membranelles and leads into the mouth. 

Examples: Spirostomum, Bursaria, and Stentor. (Fig. 77.) 

Stentor ( ) may be either fixed or free swim- 

ming. It is trumpet-shaped when attached and pear-shaped when swim- 
ming. The cuticle is striated and just beneath it are muscle fibers 
(myonemes). The nucleus is ellipsoidal, or like a row of beads. 

32. Order 3. Hypotricha ( ) Ciliata with a 
flattened body and dorsal and ventral surfaces. The dorsal surface is 
free from cilia, but spines may be present. The ventral surface is pro- 
vided with longitudinal rows of cilia and also spines and hooked cirri,' 
which are used as locomotor organs in creeping about. The cilia around 
the oral groove aid in swimming as well as in food taking. There are a 
macronucleus, often divided, and two or four micronuclei. 

Examples: Oxytricha, Stylonychia. (Fig. 78.) 

33. Order 4. Peritricha ( ) Ciliata with an 


General Biology 

adoral ciliated spiral, the rest of the body is without cilia, except in a 
few species where a circlet of cilia occurs near the aboral end. 

Examples : Vorticella, Carchesium, Zoothamnium. (Fig. 79.) 
The common members of this order are bell-shaped and attached by 
a contractile stalk. Certain species are solitary (Vorticella), others 
form tree-like colonies (Carchesium), and still others are colonial but 

Fig. 77. 

A. Spirostotnum teres (Conn). 

B. Bursaria truncatella (Conn). 

C. Condylostoma patens. (Cal- 

(From Pratt's "Manual" by per- 
mission of A. C. McClurg & Co.) 

Fig. 78. 

A. Oxytricha bit aria (Conn). 

B. Stylonychia tnytilus (Dof- 

(From Pratt's "Manual" by 
permission of A. C. McClurg & 

with an enveloping mass of jelly (Zoothamnium). The stalk contains 
a winding fiber composed of myoneme fibrils ; this fiber, on contracting, 
draws the stalk into a shape like a coil spring. 

34. Subclass 2. Suctoria ( ) Infusoria without 

cilia in the adult stage. No locomotor organs are present, and the 
animals are attached either directly or by a stalk. An oral groove or 
mouth does not occur, but a number of tube-like tentacles extend out 
through the cuticle. 

Examples: Podophyra, Sphaerophyra. (Fig. 80.) 

Ciliates are captured by the tentacles and the substance of the 

The Protozoa 



Fig. 79. 

A. Vorticella nebulifera (Bronn). 

B. Vorticella patellina (Calkins). 

C. Carchesium polypinum (Doflein). 

D. Diagram of Vorticella. The cilia at the side of the mouth have been 
omitted. (From Pratt's "Manual" by permission of A. C. McClurg & Co.) 

captured prey is sucked into the body. Both fresh-water and marine 
species are known. Podophyra is a well-known fresh-water form. 
Sphaerophyra is parasitic in other Infusoria. 

Fig. 80. 

Podophyra gracilis. (Calkins.) (From Pratt's "Manual" by permission of A. C. 
McClurg & Co.) 



THE far-reaching importance of Biology may be shown by obtaining 
an understanding of this fact : When anyone wishes to discuss 
inheritance, environment, training, or any of the many philos- 
ophies, or theories of life, some physical (biological) background must 
be found, or the discussion is not likely to impress many persons. A 
conception of such background may be gained by reviewing the following 
facts just studied : 

The little cigar-shaped animal known as Paramoecium is found in 
fresh water. It moves about rapidly by means of tiny hair-like pro- 
jections which cover its entire body. Although there are in reality only 
two reactions to any obstacle encountered, it goes forward and backward 
turning its body over and over so that its path is spiral-shaped. A groove 
extends half way down the length of the body into which particles of 
food are swept as the animal moves forward. Since the mouth is located 
at the lower end of this groove, the food is thus conveniently forced into 
it and swallowed. 

The entire animal is composed of a thick substance which appears 
something like the white of an tgg. That this thickened material is not 
homogeneous is attested by the fact that a drop of alcohol placed upon 
it causes the outer portion of the animal's body to swell up like a blister, 
while the same alcohol apparently has no effect upon the more internal 
structure. Then, too, if Paramoecia are placed in a staining fluid, two 
regions take the color much better and much deeper than do other parts 
of the body, showing that the two regions, which thus take the stain, 
are of different chemical composition from the other parts. Were all 
the substance alike, it would all stain alike. These stainable regions 
are the nuclei. 

Everyone has observed that all living things which fulfill their 
normal span of life are subject to the same natural laws, such as being 
born, growing to maturity, and dying. The nearest thing to an excep- 
tion to this general rule is found in the little single-celled animal of 
which we are speaking. This animal is not born. When it is time for 
the Paramoecium's parent to pass from this earthly region as an indi- 
vidual, the animal merely divides into two separate and distinct organ- 
isms. (Fig. 81.) 

There are now two Paramoecia where there was only one before. 
This is significant. The two new animals (each consisting of one-half 
of its parent) again divide into two separate animals, and so continue 
dividing indefinitely. The greatest number of divisions observed so far 

Interpretation of Facts 


is six thousand. This means that Paramoecia do not die, though they 
can be killed, e.g., by boiling, by immersion in acids, and in other ways. 
It means further, that every Paramoecium in existence is actually a part 
of all its ancestors; or more accurately, it is its ancestors, for these 
ancestors have never ceased to be. This must be true, because each, 
ancestor merely divided into two offspring, the offspring being in reality 

the parent itself. 
This is different 
from a parent giving 
birth to an offspring 
and then dying. 

It is an estab- 
lished biological fact 
that no living cell 
can come from any- 
thing but a previous 
living cell. No or- 
ganism or living 
thing can come into 
existence except 
from some previous- 
ly existing living 
parent form. 

Now, if suf- 
ficient food is given 
Paramoecia, they 
keep on dividing sev- 
eral hundred times; 
but, if they are with 
others of their kind, 
an interesting event takes place. Two of the animals will swim around, 
finally attaching themselves to each other lengthwise, while the wall of 
each animal which is in contact with its mate seems to disappear, the 
two animals becoming almost, but not quite, one. 

The smaller colorable spot in each animal now begins to divide into 
two parts as shown in Fig. 81. These parts again divide, making four 
pieces of each nucleus. Three of these pieces disappear (probably are 
dissolved in the body substance). The one remaining piece then divides 
into two pieces, one of which remains more or less stationary, while the 
other (often partially connected with the first) moves toward the mid- 
line of the two connected animals to meet with a similar movable piece 
of stainable matter from the attached individual. The two pieces of 
movable, stainable matter become one for a short period, seemingly 
exchanging some of their substance. Then they again separate and form 
a nucleus like the one from which they sprang. 

The animals themselves now separate, and each divides into two 
new animals. These again divide, such division continuing as already 

Fig. 81. 
Stages in the conjugation of Paramoecium caudatum. A, Stage A, 
the micronucleus in each gamete preparing for division. B, Stage B, 
the daughter nuclei in each gamete dividing. C, Four micronuclei in 
each gamete. D, three of the four micronuclei are disintegrating; the 
surviving nucleus in each gamete has divided to form cf, the male, 
and 9, the female pronucleus. F, The male pronuclei crossing over. 
F, Conjugation effected; separation of the gametes and division of 
the combination nucleus. (After Maupas.) 

160 General Biology 

mentioned, several hundred times, until this same conjugation or joining 
process occurs again. The larger stainable spot is dissolved at the time 
of conjugation and is. thought to have some nutrient function. 

It is the nuclear material which seems to be the important physical 
matter in the formation of any living thing — plant or animal — and, in 
turn, it is only the colorable matter inside the nucleus known as chro- 
matin, which breaks up and divides (the separate parts are now called 
chromosomes), and is carried on from parent to offspring. The chromo- 
somes are now considered the most important factors which throw light 
on the many problems of inheritance — that is, on all problems pertaining 
to characteristics actually obtained from our parents, whether these are 
physical, emotional, or intellectual. 

It is, therefore, of decided importance that we obtain a clear con- 
ception of chromosomes, because in the final analysis every detail of 
what we are and can be, that has any relation whatever to our physical, 
emotional, and mental makeup, must come from our parents through 
the chromosomes in the egg cell of the mother and the sperm cell of the 
father. In other words, the chromosomes that were ours at the moment 
of mixture of sperm and egg, possessed the sum total of all the factors 
producing the physical, mental, and emotional endowment with which 
we were possessed when ushered into the world (except the food and 
environment needed for growth, and a place to grow). 

In Paramoecia, the animal does not inherit anything from its parent 
— it is half of its parent. Each Paramoecium is thus equivalent to an 
egg cell or a sperm cell. The offspring is not a chip from the old block — 
it is half the block. 

An interesting application follows : 

In every living thing, where observation of chromosome material 
has been possible, life begins from a single cell of some kind. In the 
higher forms, this (egg cell) receives one half the chromosomes from 
the sperm after the egg cell has cast out one half of its own chromo- 
somes. There is thus a constant trend toward forming an individual 
who approaches the average individual of the species to which each such 
individual belongs, for, each new living thing is made up of one half 
the chromosomes which the maternal egg cell possessed, and one half 
of those which the paternal sperm cell contained. 

If this were not so, then those cases in the animal world which 
have virgin birth, would have an ever lessening quantity of the chromo- 
some material in each next generation. Each offspring would then 
become more unlike its parent, until in time, when no fertilization takes 
place to restore the proper quantity of chromosome material by a pater- 
nal sperm cell being added to the maternal egg cell, the offspring would 
not be recognized as a member of the species to which its ancestors 

In every female, in the higher forms, at the time of birth the sub- 
stance of the germ tract is already segregated so that practically every 
egg in her body that she will ever have is present. This is as true of 
a bird as of a human being. The human has about 35,000 eggs in each 

Interpretation of Facts 161 

of the two ovaries, though only about 100 to 200 of these actually ripen 
and pass out of the body during the sexual life of the individual. This 
means that the mother has little or no influence on the formation of the 
egg, because it is already complete by the time she is born. 

The eggs lie dormant and do not begin to ripen until sexual life 
begins (averaging from twelve to fifteen years in the human being). 
But, when an egg ripens, an interesting process takes place. The egg 
is expelled from the ovary immediately and, just as Paramoecia split 
into two parts, so does the egg. But the egg does not divide equally. 
A little piece, called the polar body, separates from the main part of the 
egg. This polar body may divide again, but even so, it deteriorates and 
cannot be seen in a short time. The stainable nuclear material breaks 
up into a number of chromosomes just like the chromatin of the Para- 
moecium. One half of these chromosomes remain in the larger portion, 
the other half passes into the polar body to deteriorate with that part. 

The head of the male cell (spermatozoan) is practically all nuclear 
material and goes through approximately the same process as the egg, 
except that the sperm divides equally as to size, thus forming two definite, 
living sperm cells where there was only one before — again, this is quite 
like Paramoecia. And here, too, the chromosomes divide equally, so 
that each sperm has only one half the full number of chromosomes it 
had before it divided. 

As practically all plants and animals come into existence in prac- 
tically the same way, through uniting a single cell of the male and a 
single cell of the female, we see that this is nature's way of bringing 
together the normal number of chromosomes needed to make a com- 
plete individual. Thus, each individual comes into possession of one 
half the traits or capacities of each parent cell (not necessarily one half 
of the traits or capacities of the parent) from which he sprang. Were 
this not true, all of us would be quite unlike our parents, because we 
would be less than either parent, instead of taking one half from each 
parent, thus becoming a complete human being. As our parents can 
give us but the single egg cell and the single sperm cell, everything 
else being merely food and environment, everything we can possibly 
inherit must be present in the fertilized egg. The precision with which 
the cell divides its chromatin equally between the two daughter cells 
in mitosis indicates the importance of the chromosomes. In fact, it has 
been shown that these bodies are the all important part of the cell from 
the point of view of heredity, as they are the carriers of the genes. The 
cytoplasm seems to play but a small part in the role of heredity. 

For anyone wishing to study life, therefore, the study of chromo- 
somes looms up as the most important factor. 

The laboratory study of the fertilized cell, of which we speak, has 
shown that each such fertilized cell divides into two cells ; these two 
into four; each of these four into two, making eight; these eight into 
sixteen ; and so on indefinitely until the entire body has finished its 

162 General Biology 

The first group or sheet of cells becomes a hollow sphere called a 
blastula. The blastula continues growing, which means that this single- 
layered sphere indents, and this indentation extends into the sphere until 
two layers of cells are formed. This is called the gastrula stage. Ani- 
mals having two layers stop growth when this stage is reached, while 
all higher forms produce a third layer of cells between these two. 

Every living animal passes through one or more of these develop- 
mental processes. This fact led so many of the early biologists to sup- 
pose that each developmental stage meant that each one of the higher 
forms of animals must have sprung from those which stopped in the 
one- and two-layer stage just beneath the higher form. It means, how- 
ever, that all living forms pass through a similar state of growth. 1 

Very early in this development of an Qgg, after it begins to grow 
(fertilization apparently furnishes this growth impulse), certain cells 
divide much more rapidly than do others. The rapid-growing cells, con- 
sequently, soon surround the less-rapidly growing ones, thus forming a 
sort of protecting case or capsule for them. Now, some of the very first 
cells that are thus protected and grow into the very innermost portions 
of the growing embryo, are the egg-cells and the sperm-mother cells. 
This occurs long before one can even distinguish what kind of an animal 
the embryo is to become. 

It was Professor August Weismann of the University of Freiburg 
in Baden, who in 1892 gave the world his book, "The Germ-plasm, a 
Theory of Heredity," which has made us interpret the various facts so 
far mentioned in a different way from what had been done before. Up 
to that time men said that the reason a boy so closely resembled his 
father was because he was "a chip from the old block." Professor 
Weismann has shown us that this is incorrect, and that both father 
and son are pieces from the same block. That is, the sex-cells in both 
mother and father, being a part of the earliest differentiation in the 
growing embryo as already shown, are really placed in position in the 
child before he is born, so that a parent, simply considered as a parent, 
has absolutely nothing whatever to do with the matter, such parent's 
body acting only as a case or capsule which carries the germ-cell to the 
next generation. 

This is made clearer when it is remembered that every Ggg in the 
female is already present at the time of such individual's birth. All that 
happens during her life is a ripening, or maturing, of such tgg, and 
fertilization by the male sperm. The sperm-mother-cells which are to 
divide and form sperm, are already present in the male child when he is 
born, though they begin to divide only after puberty. 

The sex-cells are, therefore, present at birth in each person, and it 

a It does not follow that because a man builds a school, a barn, and a church, that the church 
must therefore have first been a school and a barn, even though such builder used exactly the 
same tools and similar material in the building of each structure; in fact, it would not follow, 
even though he build the foundation and the first story of each structure exactly alike in each case. 

Interpretation of Facts 163 

has not yet been proved that one can either change or add anything to 
them, unless, again it be merely the food and drink he takes which may 
or may not nourish such sex-cell properly. 

This means, then, that just as with Paramoecia, each and every 
one of us cannot obtain from our parents one more particle of physical, 
emotional, or mental ability than our parents may have had, because we 
get only what was present in the egg-cell of our mothers and the sperm- 
cell of our fathers. 

It means further, that when we go back even twenty-five genera- 
tions, considering our two parents, four grandparents, eight great- 
grandparents, etc., we are related in actual blood-relationship to more 
people than there are in the world at the present time. It means that 
just as Paramoecia are really their grandparents and all their ancestors 
in one, so we are also actually and truly our own ancestors in so far as 
our sex-cells are concerned. 

An actual living particle of every one of our forefathers is really 
present in each one of us. It means that the entire animal world, in- 
cluding the human family, by constant intermingling of chromosomes, 
is always tending toward an average, so that no matter how many cen- 
turies elapse, no real, individual, physical, or biological progress is 
possible. Always will the next succeeding generation, or at least the 
next after that, have some sex-cells in their bodies which will again pro- 
duce an average being. 

This sex-bridge which connects every human being with every 
other human being in this way, is sometimes referred to as the Weis- 
mannian bridge. It is this bridge which is both the hope of an oppressed 
people and the despair of those who would change human nature from 
what it is. We can build only upon instincts and on human desires and 
wishes which are in turn the result of the instincts we were born with. 
We may develop such instincts and desires, but no actual change in 
human nature can possibly ever come into existence. Human nature 
is the same now as it has ever been and always must be, until some 
method be obtained by which we can tell in advance by looking at a 
chromosome, what good and bad characteristics such chromosome con- 
tains, and then be able to destroy the bad therein. This means that 
we are aeons and aeons removed from any solution to our eugenic prob- 
lem on a truly scientific basis. Even then, were we able to accomplish 
this practically impossible task, we should still have to evolve some plan 
by which we could see the egg and the sperm before they unite, a task 
again practically impossible until new human beings can be grown in 
the laboratory. 

Professor Weismann also demonstrated to the scientific world that 
the germ-plasm early separates from that part which is to become the 
outer portion of the body and which is called the somatoplasm. 

The Abbott Mendel has proved that no matter how much inter- 

164 General Biology 

breeding there may be among plants or animals, there are only two types 
of offspring produced, i. e., pure stock and half-breeds. 1 The eggs and 
sperm in the germ-plasm always remain pure. That is, if a white and 
black animal mate, a portion of the eggs in the ovary of any female off- 
spring from such union will be carriers of pure black, and a portion will 
be carriers of pure white characteristics. The sperm of the male, like- 
wise, are carriers of one or the other colors, but are not themselves half- 
breed. It will be noticed, therefore, that from this Mendelian theory 
additional evidence is brought forth to substantiate the Weismannian 
theory of germ-plasm, which holds that the germ-plasm is separate and 
distinct from the rest of the body. 

The color of the skin of any offspring of black and white animals 
may be of any shade, from pure black, to almost, or entirely white. But 
the sperm and the egg have not intermingled in so far as color is con- 
cerned. The color shows up on the outer part of the body, or in what 
we call the somatoplasm. The germ-plasm always remains pure, so that 
in the next succeeding generation, if any of these half-breeds in turn 
mate with each other, we have the four possibilities of a sperm carrying 
the genes for whiteness meeting with an tgg carrying the genes of black- 
ness and again producing a half-breed, or a sperm carrying genes of 
blackness meeting with an tgg carrying genes of blackness and pro- 
ducing a pure black, while a sperm carrying the genes of blackness 
mating with an egg carrying the genes of whiteness, produces a half- 
breed, and a sperm carrying genes of whiteness with an Qgg carrying 
genes of whiteness produces a pure white. 

From observation, however, it is found that most half-breeds will 
look like one or the other of their parents in so far as color of skin, eyes, 
and hair is concerned. Whatever color the offspring shows, is known 
as the dominant color. 2 We cannot tell, however, until we observe the 
first brood of half-breeds which is the dominant color. 

We do not know why one characteristic is thus dominant, but the 
important thing to remember is that this entire possibility of any of 
the four possible matings mentioned above taking place in any mixed 
offspring, is all a matter of chance. Having observed thousands of in- 
stances of this kind among both plants and animals, scientific men now 
accept it as a fact that we do obtain two individuals of pure stock, and 
two half-breeds from matings of mixed ancestry. It will be noticed 

1 This refers to the crossing of two pure breeds, of course. 

^Recessive is the word set in opposition to dominant. A recessive characteristic is always pres- 
ent in the germ-plasm of an animal or plant of mixed ancestry, but it does not show in the 
somatoplasm — in any part of the body proper outside the germ-plasm. The dominant character- 
istics cover up the recessive characteristics. For example, in half-breed offspring'. — a cross between 
white and black parents — if all these half-breeds are black, we call black the dominant charac- 
teristic as to color, though such half-breed has just as much white in him as he has black. The 
white which is present but which is not seen is called the recessive characteristic. 

It is very important, however, to remember that in so far as the germ-plasm — the sex cells 
themselves, that is, the eggs and sperm — is concerned, each egg and each sperm has, roughly speaking, 
one-half black and one-half white characteristics ; but the dominant characteristic is the only one 
which shows, and that only in that part of one's make-up zvhich is not germ-plasm. 

To clarify the matter; if half-breeds, which are the offspring of black and white parents are all 
black, we call black the dominant color. 

Interpretation of Facts 165 

that this is pure chance, there being approximately half as many carriers 
of either color in each sperm of the male as there is in each egg of the 
female. Therefore, there is just as much likelihood at any given time 
of a sperm carrying blackness meeting with an egg carrying whiteness 
as of one carrying whiteness meeting one carrying blackness and vice 
versa. But it must not be forgotten that not only the half-breeds, but 
also the pure bloods of the dominant type will all probably look alike 
as to color. This appearance of the same color in the half-breeds, which 
appeared in the dominant pure-blood, is the thing which confused men 
for many years, and it was only after Abbott Mendel gave us his explana- 
tion that we have been able to understand why this is so. 

Mendelism has also added some interesting biological speculations 
to the earlier ideas of naturalists. 

If we define species as meaning all those particular plants and ani- 
mals which can interbreed and in turn give birth to fertile offspring, it 
can be seen immediately that we cannot have any new species at all. 
For, if the offspring of such plants or animals can give birth in turn 
to other offspring, they belong to the same species as do their parents, 
and, if they differ in appearance from their parents, they can only be 
called variations of the parent species. If they do not interbreed, or, if 
after interbreeding, they give birth to non-fertile offspring (such as the 
mule, which is the non-fertile offspring of a mare and a jack), then, of 
course, there can be no further offspring, and we can have no further 

Mendelism has added a very important and interesting fact to such 
theorizing. For example, in the dominant type of offspring of pure-bred 
parents, there are always pure sperm and eggs which carry recessive 
characteristics, so that it follows, that at any time in the future, if by 
chance such pure egg and sperm meet, a totally different type of plant 
or animal may be produced. But this may be merely the coming forth 
of a plant or animal similar to some ancestral form, which was the result 
of two germ-cells meeting that carried the recessive trait. Therefore, 
although these recessive germ-cells were always present in all ancestors, 
they were covered up in so far as external characteristics are concerned 
by the dominant characteristics. A new species, such as this which 
comes forth suddenly, is called a "sport" in nature, and the theory that 
all new forms come forth in this way is called the mutation theory. 
But, as these so-called new forms may be explained as being recessives, 
again coming forth after lying dormant for ages, there may be here no 
new species at all. 



WITH a clear understanding- of what has been said regarding 
the division of chromosomes in maturation, in a former 
chapter, and the discussion of interpretations in Chapter X, 
we are in a position to understand the terminology of heredity, genetics, 
and Mendelism, which is met with quite commonly in modern biological 

While genetics really means the "origin of things" it has come to 
be used as the name of that science which studies the ways and means 
by which minor inheritable characters can be judged. It must never be 
forgotten that to inherit anything from one's parents in the biological 
sense, means that the "something" which is inherited must already be 
present in the egg of the mother, or the sperm of the father, or in both 
these germ cells, at the time the egg is fertilized. Every factor that 
may influence an organism, which is not already present in the gametes, 
is due to environmental conditions and cannot be said to be inherited. 

At this point we must also remember the distinction made in a 
former chapter that germplasm and somatoplasm are entirely separate 
and distinct. 

Mendelism, or rather Mendel's "law," merely means that each char- 
acteristic that we may inherit must be considered as a single unit. To 
illustrate, we must not think of a child as inheriting its father's hair 
because it has dark curly hair like its father, but we must think of dark- 
ness in color as one character of inheritance and curliness as another; 
for, a child may inherit the darkness in color from its mother and the 
curliness from its father. 

Thinking in terms of unit characters will throw much light upon 
many of the interesting problems of life. We may thus account for one 
artist, for example, having a very decided sense of form and another of 

It is now generally conceded by biologists that acquired character- 
istics are not transmitted to the offspring. We know, however, that 
brothers and sisters of the same family differ from each other in many 
respects. We know that no two leaves of grass are exactly alike; in 
other words, that all living things springing from the same parents vary 
somewhat from each other. It is the purpose of genetics to find the 
mechanism by which such variation takes place, and then to be able 
to apply the knowledge thus gained toward bringing about the types of 
variations one wishes. Every variation represents a single unit charac- 
ter or a combination of these unit characters. One may use as an exam- 
ple the various species of cattle. Cows of a certain breed may produce 

Genetics 167 

a very rich milk but not a great quantity. Cows from another breed 
may produce great quantities of less rich milk, while those of still 
another breed living in the tropics may be more or less immune to heat 
and tropical disease. If one wishes to bring cattle into a rather hot 
clime, it will, therefore, be to one's advantage to obtain that breed which 
will produce the greatest quantity of rich milk and likewise be able to 
withstand the great environmental change necessitated by removal from 
a temperate or cold clime to one of great heat. 

We have already seen that the inheritable characters are contained 
within the chromosomes. The definite factors, whatever they may be, 
which carry the unit characters within the chromosomes, are called 

From our knowledge, at the present moment, of the way the chro- 
mosomes divide in cell division, and the way they throw off one-half 
of their number during maturation just before fertilization so that fer- 
tilization can again restore the regular number, we are led to believe 
that no unit character can be inherited unless a gene from the father 
and a gene from the mother unite in the chromosomes. 

We may say, for example, that all the unit characters, which any 
individual can possibly inherit, are contained within the chromosomes of 
the germplasm of its parents ; that each chromosome may contain thou- 
sands of genes which may occur in any combination, the individual him- 
self actually inheriting only those unit characters which happen to be 
the result of the particular gene of paternal and maternal chromosomes 
which met at the time of fertilization. . 

To make this clear let us assume that a white and black guinea 
pig are mated. The whiteness and blackness that we see, lie, of course, 
in the somatoplasm ; but, in order that either color be inherited, there 
must be genes in the chromosomes of the germplasm which determine 
the somatic character of whiteness and blackness. We know that, if a 
black guinea pig is mated with another black guinea pig, both of which 
are in turn the offspring of an entire race of black animals, that only 
black guinea pigs will be produced. However, if a black and white 
animal mate, the offspring are really half-breeds in regard to their 
germ-cells, though their somatoplasm may show some variation in color. 
We, therefore, assume, from the experimental evidence obtained through 
breeding experiments of many kinds, that in order to produce a black 
animal, both the paternal and maternal genes, which carry the determi- 
nation of color, must have carried blackness. In the production of a 
half-breed, one of the genes determining color must carry whiteness 
and the other blackness. (Fig. 82.) 

In other words, two genes always meet to produce any character 
sufficiently powerful to be carried on, in turn, through succeeding gen- 
erations. The character which is thus carried on and which shows itself 
in the somatoplasm is called dominant. Blackness would thus be 
dominant when a white and black animal mate and produce half-breeds 


General Biology 

which are all black in color. However, as has already been stated, the 

color is only in the somatoplasm, 
germplasm remains pure; that is, 



.•J Ufh 

E Y .. 



>/ W. 

Fig. 82. 

Diagram of two chromosomes, each square 
representing a gene. 
An insect, for example, with these two 
chromosomes would possess a normal 
wing, a miniature wing, a rudimentary 
wing, and forked bristles. All these char- 
acters could be transmitted to the offspring. 
The insects' body and eyes, however, 
would be heterozygous. 

It is important to remember that the 
some of the eggs in the mother and 
some of the sperm in the father will 
be of the black variety, and others 
will be of the white variety. To put 
this in other words, there will be no 
half-breed eggs or sperm. 

Whatever unit character shows 
up in the somatoplasm in animals 
of different breeds, is said to be 
dominant, while that unit character, 
which is present in the germplasm 
but is not seen in the somatoplasm, 
is said to be recessive. 

In our example of the mating 
of a white and black guinea pig, the 
offspring, though black, have white- 
ness in their germplasm even if it 
does not show externally in the 
somatoplasm. Blackness in this 
case is, therefore, dominant; white- 
ness, recessive. 

In their accounts of breeding ex- 
periments, geneticists use a formula 
to represent dominant and recessive 
genes. The capital letter represents the dominant gene and the small 
letter the recessive. In the example we have been discussing, the capital 
letter — B — will represent the gene which carries blackness, the domi- 
nant color; and the small letter — w — will represent the gene carrying 
the recessive white. The formula in our example of a half-breed black 
and white, therefore, is — Bw — . 

In those cases where pure blooded blacks would meet with pure 
blooded blacks, the formula would be BB, while in the breeding of two 
pure whites, the formula would be WW. It will, therefore, be noted 
that we may have the various formulas BB, Bw, WW, Wb, provided, 
of course, that a recessive black could be found. 

Wherever two genes are alike, so that either has BB, or WW, the 
resultant zygote is called a homozygote, while the organism resulting 
from a homozygote is said to be homozygous. If the two genes of the 
mating pair are different, such as Bw or Wb, the zygote is called a 
heterozygote, the resultant animal being called heterozygous. It is, of 
course, quite common for the same animal to be homozygous for some 
characters and heterozygous for others. 

The parents are often represented by the capital letter P. The first 

Genetics 169 

generation (which means the offspring from these parents) are repre- 
sented by the formula, F x . The offspring of F x in turn are known as 
F 2 , and so on, the F representing a filial generation. 

In many cases the various characteristics, which the genes deter- 
mine, may be independent of each other; but, just as certain chemical 
elements have an affinity for each other, so there are various types of 
characters that often link themselves in the same way. This is known 
as linkage. Color of hair and the direction in which the hair grows, 
such as curliness, straightness, or whorls, are often linked. Then there 
are also certain types of sex linkage by which we mean that there are 
certain characters, such as plumage in fowls and eye-color in flies, which 
are almost always concomitant with the sex of the individual. 

Much has been written on sex-determination in the past, though 
it is only recently that any progress has actually been made in this field. 
It has been found that sperm cells possess an extra or accessory 
chromosome (called an X-chromosome by American writers, and a 
heterotropic chromosome by Europeans). (Fig. 30, A.) When such a 
sperm cell fertilizes an egg, a male is produced, while, when an egg 
containing the regular even number of chromosomes is fertilized by a 
sperm with an even number of chromosomes, a female is produced. 

Interpreting these findings of the cytologists, biologists now believe 
that there is such an extra chromosome in both egg and sperm, but 
that in the egg, this X-chromosome divides as do the others, although 
this division is delayed until some time after the other chromosomes 
have divided in the maturation divisions. This means that the 
X-chromosome of the sperm is really a double chromosome which fails 
to separate during spermatogenesis and consequently goes over to one 
of the two sperm-cells entire. 

Then, in some organisms this X-chromosome has actually been seen 
to be made up of a larger and a smaller portion, while in the female of 
the same species both parts of the chromosome are of equal size. When 
the accessory chromosome is thus divided into two parts of different 
sizes, the smaller is called the Y-chromosome. 

It follows from this that, if unit characters are carried by the genes 
of the X-chromosome, all organisms in which the sperm carry an 
X-chromosome, must necessarily transmit the characters of the X-chro- 
mosome to the female offspring only, while females can transmit them 
equally to all offspring. Similarly in those organisms in which eggs 
may lack one chromosome, the female can transmit characters only to 
their sons, while males can transmit to their offspring of both sexes. 
This is the explanation of sex-linked transmission as shown in men who 
are color-blind. Such men transmit this defect to their daughters, and 
the daughters can in turn transmit it to all their sons and daughters. 

There are exceptions to this. A usual sex-linked characteristic such 
as color-blindness, is sometimes transmitted from father to son directly. 
This is explained by Bridges as being due to what he terms a "non~ 

170 Geneeal Biology 

disjunction" of the sex-chromosomes in the polar divisions of the egg 
during the maturation division. In other words, such a non-disjunction 
may come about by the two X-chromosomes in the egg pairing but then 
failing to separate, so that either both remain in the mature egg or both 
are extruded with the polar bodies. 

In a study of parthenogenesis (virgin-birth) further evidence is 
brought forth in regard to the function of the X-chromosome. For 
example, there may be one maturation division without a reduction of 
chromosomes. In this case the single polar-body and the egg nucleus 
will both contain the diploid number of chromosomes. This is quite 
common in the Crustacea and a few other forms. 

Or, there may be two polar divisions, after which one of the polar 
bodies reunites with the egg nucleus. Here, again, the full number 
(diploid number) of chromosomes is found. 

Or, in some forms (Hymenoptera and the male-producing eggs of 
Rotifers), two polar divisions really take place, which reduce the chromo- 
somes to the haploid number. If these eggs are unfertilized, they give 
rise to males. Such eggs already have only half the full number of 
chromosomes. Consequently in their germ cells, in turn, there is no 
further reduction. The first spermatocyte division in these is really 
suppressed. If the eggs are fertilized, they produce females. 

In those Hymenoptera where there are two divisions, but the 
chromosomes divide at the equator and not longitudinally, the diploid 
number is retained, and females are usually produced. 

Various other evidences of great value and interest will be found 
in the books on Cytology mentioned at the end of this chapter. 

The diagram of the chromosome-cycle of Phyllaphis coweni (Fig. 
83) will throw light on this subject. 

The top group shows a fertilized egg with four ordinary chromo- 
somes and two X-chromosomes. Three lines of descent pass downward 
from the egg. On the left, this line of descent leads to a female which 
will produce a sexual egg. The central line of descent leads to a female 
which will reproduce parthenogenetically, and on the right the line of 
descent leads to a male. 

The second and third groupings from the top represent the meta- 
phase groups as well as the diagrammatic anaphases of three eggs, of 
which the left and middle will produce females, the right a male. In 
the female-producing eggs, the X-chromosomes divide at the equator 
and not longitudinally ; while in the male-producing eggs they pair and 
separate so that the male has only one X-chromosome. 

The fifth grouping from the top at the left, is the metaphase group 
of the first polar division of the sexual egg. All the chromosomes are 
paired. Below this, the anaphase of the first, and the telophase of the 
second polar division, leave three chromosomes in the egg. 

The fifth grouping on the right is the metaphase group of the first 
spermatocyte division with paired regular chromosomes and a single 



X-chromosome. Below this, the diagrams of the first (unequal) and the 
second (equal) spermatocyte divisions, leading to the ultimate sperm- 
cell with three chromosomes and a small degenerate cell with two. 
When the egg and sperm again unite in fertilization, the original six 
chromosomes are restored, and the egg is again as we see it at the top. 
From what has been said, it can be plainly seen that in all organ- 


io«tv @@ 






Fig. 83. 

Diagram of chromosome-cycle of Phyllaphis coweni. 
(After Doncaster.) 

See text for explanation. 

isms where there is an X-chromosome, this extra particle (as it does not 
divide as do the other chromosomes) must result in some sperm-cells 
having an even number of chromosomes and others an odd number. 

For example, let us say there are twenty-one chromosomes in the 
original germ-cell from which the sperm is to develop. One of the newly 

172 General Biology 

forming sperm would possess ten and the other eleven chromosomes. 
The regular somatic number of chromosomes in such an organism 
would be twenty-two. The egg will, therefore, regularly divide and 
throw off eleven to obtain the haploid number. Those eggs, which are 
then fertilized by a sperm containing ten chromosomes, become males 
(as the diploid number in such a case would again be twenty-one) and 
those eggs fertilized by a sperm containing eleven would possess the 
full somatic number of twenty-two chromosomes and become a female. 

This means that in those cases where there are X-chromosomes, 
the odd chromosome never pairs in the maturation division with another 
chromosome, nor does it produce a tetrad. It simply passes undivided 
to the daughter sperm. 

References : 

L. Doncaster, "An Introduction to the Study of Cytology." 

W. E. Agar, "Cytology." 

W. E. Castle, "Genetics and Eugenics." 

East and Jones, "Inbreeding and Outbreeding." 



IN no branch of study is the student confronted with more difficulties 
in the way of separating fact from interpretation, and explanation 
from description, than in the field of Animal Psychology, and this, 
notwithstanding the fact that Animal Psychology owes its entire value 
to its ability to explain and not to describe. 

The tendency of the human mind to read into an animal's actions 
the same motives and reasons that cause man to react in a similar man- 
ner is difficult to overcome. In fact, a definite word, anthropomorphism, 
is in common use among psychologists to describe just this tendency to 
humanize animals. 

Still, the only way we have of interpreting the behavior of an 
animal must be in terms of human understanding, for we have neither 
language nor imagery which can bring to us the sensations, emotions, 
and driving force of an organism so totally unlike ourselves as an insect, 
for example. 

As one writer has said, anger with us is always associated with an 
increase in heart beat and a more rapid breathing, and our nerves are 
all "set on edge," but an insect has a totally different set of blood- 
vessels, an entirely different breathing apparatus and a different nervous 
system. What are its accompanying sensations when it feels angry? 
In fact, a wasp often bites off its own abdomen when angry. How can 
we, when our respective organisms are so unlike, know much about how 
such animals feel? 

Further, all of us have observed that probably most plays and 
novels hinge their plot entirely on some misunderstanding. If human 
beings, who have a common language to make themselves understood, 
are so frequently misunderstood, how much more will we not misunder- 
stand and misread the actions of animals entirely unable to tell us any- 
thing in terms which are understandable to both ? 

It is for reasons of this kind that many throw up their hands in 
despair and insist that we never can know anything at all about the 
animal mind, but that if we wish to establish an animal psychology 
anyway, there is only one way to go about it, and that is, merely to. 
study the behavior in the laboratory under set conditions so that we 
can learn just how each animal reacts to a given stimulus. Such a 
method assumes that all .animals of the same sex, of the same age, and 
in the same state of health, will always react in exactly the same way 
when the same stimulus is applied under the same conditions. 

174 General Biology 

We shall go on from this point a little later, after the student under- 
stands several important terms. 

Objective and Subjective are two of the most important terms used 
in psychology. The former is the term applied to all things which come 
under the senses. That is, a thing is objective when it can be observed 
and measured in the laboratory. It is anything, in other words, which 
occupies space. Subjective refers to those things which make no 
observable difference in space and which cannot, therefore, be measured 
in terms of the rule and scale of the laboratory. For example, changes 
in the mental world, such as thought and feeling, are subjective. In the 
classic sense, subjective means the act of the mind itself or what is in th2 
mind, while objective refers to the matter with which the mind works. 

An illustration of these two terms, as they are commonly used, 
comes to mind. Suppose a neurologist were to examine the optic nerve 
and the optic centers of the brain of a student while the latter is reading 
a letter. The neurologist could probably tell that the optic nerve and 
center were functioning, but he could never tell what the letter con- 
tained, nor could he see what emotions were called forth in the mind 
of the student. The movement in the nerve and nerve center would be 
objective, while the emotional impression made on the student would be 

Not only would the neurologist be unable to observe the emotional 
impression made upon the student, but he would be unable to tell why 
certain vibrations which, so far as observation goes, are all alike, should 
produce sensations of red or green in one case, and another color in 
another case. 

All our emotions, longings, ambitions, thoughts, and ideas, so long 
as they remain mental states, are subjective, while when they express 
themselves as acts, they become objective. 

Psychology is the study of the subjective world. The word 
Psychology (Greek psyche=soul-f-logos=discourse) actually means 
the study of the soul, but since laboratory methods have come into 
existence in psychology, and laboratory men think only in terms of 
measurable substances, it is commonly said to be the study of mental 

Since the laboratory methods of studying everything objectively 
under set conditions has made its way into psychology, the workers in 
this field have become divided into various camps or schools. First, 
come the Behaviorists, who insist that the results of mental activity are 
actions and reactions to given stimuli, and it is only these results which 
can be measured, and which, therefore, may validly be used as data on 
which to form any theories of the mental life of animals. Second, come 
the Introspectionists, who follow the classic method of antiquity. They 
insist that the only real way of studying mental life is to introspect — 
to look into our own mental life and try to understand how and why 
we do what we do under varying conditions. They insist that we must 

Animal Psychology 175 

analyze our own thoughts, motives, and emotions, and then, if an animal 
has an organization quite like our own, we may validly assume that it, 
too, functions somewhat like our own. 

Since extremists on any side of a discussion are likely to go astray, 
it is always best not to follow entirely any single group to the exclusion 
of another. To be fair, one must use anything and everything that will 
throw light on the problem one is trying to solve. 

The word Mind is another confusing term.- By the older writers 
it was used to designate the personality of an individual. That is, if one 
say with Descartes, "I think" therefore "I exist," the "I" which does the 
thinking and which does exist is the true personality, the true mind. 
Or, one may note that it is quite common to dream that one has died 
and attends one's own funeral. That which can look at its own physical 
body as the physical co-partner of the true ego — of the individual's per- 
sonality — is the mind, or as the older writers called it — the soul. 

Not only do we here see a distinction of the ego, or personality 
proper, as mind, but we also note that the mind is separate from the 
thoughts which the mind brings forth. We can, therefore, understand 
these writers when they tell us that the brain is in turn the organ of 
the mind, but not the mind itself. 

The average laboratory man will have little of this, however. He 
insists that mind does not exist as distinct from thought and emotion. 
He means by mind the whole "stream of consciousness" of the indi- 
vidual — all thoughts such as one has ever had, plus all one's emotions, 
such as pleasures and pains — accumulated experiences of the individual, 
in other words. 

The laboratory men do, however, admit two divisions of this mental 
life, namely, consciousness (awareness) and feelings (emotions or affec- 
tions, such as pleasure and pain). 

The student can understand these two divisions easily if he will 
think of breaking a bone in his body. It is one thing to know (be 
conscious of) that the bone is broken, and another thing entirely to feel 
the pain it may cause. 

The idea of a difference between the mind and the physical body 
containing it, leads us to note the distinction between mind and matter. 
Those who accept this distinction are called dualists. 

Great conflicts have been waged by the learned of all times as to 
which is the more important of the two — mind or matter — and which 
was first upon the scene of existence. Some have contended that mind 
(spirit) came first, and this, then, was the cause of the physical universe 
(matter). Such contenders are known in philosophy as spiritualists. 
Others contended that matter was first on the scene, and that mind was 
late in its arrival, because it is only an emanation of some kind from the 
physical. That is, mind is something like the secretions from ductless 
glands which we know little about, but which we do know exist. Such 
men are called materialists. Yet another group insisted that as mind 

176 General Biology 

and matter are always together, neither may be given the preference. 
Both are different sides of the same coin. Each thought-wave is always 
associated with a nerve-wave of some kind, and neither can exist with- 
out the other. Such men are called monists. It will be seen that the 
term "monists" is applied to this group because they do not accept a 
dualism in life. 

These different groups of contenders attack psychological problems 
with different prepossessions. The spiritualist is likely to call himself 
an interactionist in psychology, the materialist a behaviorist, and the 
monist a parallelist. 

As it makes a profound difference to a patient which one of these 
theories his physician holds, the student must know what each term 
means, or he will be totally unable to pass judgment on the many and 
conflicting discussions which are ever coming before him. 

The interactionist holds that the state of mind of an individual can 
and does influence his physical being and vice versa. An example of 
this is a man worrying over financial losses, whose body becomes run 
down until disease clutches him. 

The behaviorist insists that only a definite physical reaction, meas- 
urable in the laboratory, is valid data on which to base a scientific 
conclusion, and that until the individual mentioned above shows a definite 
measurable reaction, there is no change which we as scientists can use 
or accept. 

The parallelist, insisting as he does that both the mentality and the 
physical organ which is associated with it, are different sides of the same 
thing, must necessarily consistently claim that the mind is totally unable 
to influence the body and the body totally unable to influence the mind. 
In fact, one prominent parallelist says that one may as well expect a 
piece of beefsteak put into a sausage machine to come out a moonlight 
sonata as to expect either body or mind to influence each other. 

It is, therefore, only the interactionist who can consistently speak of 
nervous and mental diseases, and who can consistently use both physical 
and psychic remedies. 

At this point we may consider what is commonly designated as 
structural and functional psychology. 

Structural psychology concerns itself with (1) the general organi- 
zation of an organism, (2) the general organization of its nervous sys- 
tem, and (3) the organization of the specialized nerve parts, such as the 
eye, ear, nose, etc. 

Functional psychology is interested in (1) the general way an 
organism reacts (discrimination), (2) whether the organism can modify 
its action (docility), and (3) in how many ways and in what way its 
behavior will vary (initiative). 

Again the student must be cautioned not to let one side of a prob- 
lem cause him to discard much that is of value in opposing schools of 

Animal Psychology 177 

Just as those who are primarily interested in nothing but anatomy, 
are likely to leave out important functional causes in a disease, so those 
primarily interested in physiology are likley to forget the structural 
elements which may contribute points of tremendous importance. 

All schools of science have been drilling into the student the sup- 
posed "fact" that "structure determines function," but since the very 
recent work of Carey, who converted unstriated bladder-muscle of a 
living dog into living heart-muscle by simulating heart conditions in 
the bladder, we must insist that function has just as important a part 
in changing and determining structure as structure has in determining 

However, we must not forget that even in the case just mentioned, 
the substance to be changed was already present and must have pos- 
sessed the potentiality of change before it could be worked upon. 

With this introduction we can the better understand the two ways 
in which the study of comparative psychology is approached by the 
modern laboratory worker. First, we may take a highly developed 
individual, such as man, and after analyzing his mental world, apply 
the knowledge thus gained to the lower forms, or 

Second, we may follow up, step by step, the increasing learning- 
ability on the part of all phyla of animals, beginning with the unicellular 
and passing upward through an ever-increasing scale of ability. 

It is this second method which seems to have found most favor with 
animal psychologists. 

But, in reading works on animal psychology, one is always con- 
fronted with a great confusion of terms. In fact, one finds here the 
same difficulties that confront the student in any of the biological 
sciences. The first workers in all these fields were philosophers, and 
were interested primarily, and sometimes only, in the human family. 
The terms, therefore, which these men used, although worked out with 
great precision, applied only to man. 

The newer writers took many of the older labels and placed them 
on new bottles, so to speak. This has caused a world of confusion, not 
only to new students, but to many well versed in language and literature. 

Such words as Mind, Intelligence, Reason, Memory, Consciousness, 
Sensory or Associative Memory, Instincts, and Reflex Actions, are some 
of the terms which the student must use, and which have many con- 
flicting meanings in modern literature. It is imperative that the student 
obtain a clear and concise definition of these terms and use them only 
in this restricted sense. Then only can he understand the meaning 
which different writers assign these words, and then only can he know 
whether they are calling other things by the same name, or giving 
different names to the same thing. 

We shall have to speak of Instincts immediately, so it is well to 
begin with this term. Instincts are defined as inherited tendencies in 

178 General Biology 

an organism which cause protective reactions when harmful stimuli are 
applied. For example, a frog, even after both cerebral hemispheres are 
removed, will still scratch the part of its body to which a drop of acid 
is applied, and it will even snap at and swallow a fly which has been 
placed on the tip of its nose. Again, a fly will walk, fly, and clean its 
legs and wings, after its head is entirely removed, and the writer has 
kept a decapitated cat alive for many hours by artificial respiration and 
caused it to perform many instinctive actions such as scratching itself, 
waving its tail, etc. 

In order to understand Reflex Action, 
it is first necessary to know the meaning of 
a Nerve Arc (Fig. 84). This latter is 
merely the entire nerve-path over which an 
impulse passes to a nerve-center and out 
again to a muscle cell. It must, therefore, 
consist of the nerve-ending of a sensory 
Fig. 84 Diagram of the path of a nerve (receptor) through which the impulse 

simple nervous reflex action. . . 

is received, and the sensory nerve-fiber 
which carries the impulse to the nerve-center to join at this point with 
a motor-nerve fiber which in turn carries the motor impulse to the 
motor-nerve-ending (affector). This motor-nerve-ending is always 
located in some muscle fiber. Psychology textbooks often speak of a 
nerve-arc, as "a perception with a motor impulse." 

A Simple Reflex Action is one that passes over such a simple nerve- 
arc without first passing to the higher nerve-centers, or, we may say, 
one which does not come into the consciousness of the individual in 
whom the action takes place. Such a reflex action is, therefore, purely 
physical. There is no need of assuming any mental state or sensation 
as an accompaniment. 

When an individual is born, his nerve arcs are set in some form 
or another, so that with one individual the same stimulus will cause 
quite a different reaction, than it will in another. But, just because 
fhese nerve-arcs are set in the way they are, the same nerve-arc will 
always react in the same way to the same stimulus, if all other condi- 
tions are equal. For example, a child may have grown accustomed to 
saying "I is" for "I am" and have said it so often that it finds it very 
difficult to correct itself. Now, if we constantly force the child to use 
the form "I am," the particular nerve-arc which carried the "I am" 
reaction will become relatively stronger than the one which carried the 
reaction "I is," and then, and not until then, does the latter phrase 
become a sort of second nature to the child. 

So, too, a puppy that has the vicious habit of snapping at passers-by, 
can be made to react differently by giving him a whipping several times, 
immediately after he does the undesirable act. 

Animal Psychology 179 

In both these cases memory enters, but only a simple sensory mem- 
ory (association memory) which has little to do with any thought. The 
impulse (inner stimulus) in the puppy to snap, is great, and so the 
"snapping nerve-arc" carries the impulse and the snapping is done ; but 
the punishment, which has been meted out, has set up an impulse of an 
opposing nature, and as soon as this latter becomes the stronger impulse, 
the puppy has been trained. 

We may say in this case, that the puppy has the desire to snap, and 
the nerve-arc, which carries this snapping-impulse, begins to function. 
But the whipping has caused a new nerve-arc to function at the same 
moment, so that a third nerve-arc, that of inhibition, comes into play 
and the animal does nothing. This is quite similar to the reaction of 
persons in hypnosis. Here an individual is told he cannot bend his arm. 
The impulse not to bend the arm is just as strong as the one to bend it, 
so no movement takes place. 

An impulse is defined as an inner stimulus. 

It is well to bear in mind the foregoing paragraphs as these show 
the possibility of two opposing impulses and even two opposing reactions 
taking place at one and the same time over different nerve-arcs. Often 
we read of lower organisms possessing discriminating powers of various 
kinds which can be interpreted in quite different ways from what the 
writer of such an account would have us believe. We need only 
remember that there can easily be one set of nerve-arcs functioning 
for the acceptance of food and another set for the rejection of it, so 
that it depends on which set carries the stronger impulse as to whether 
the animal accepts or rejects the food. It is by no means necessary to 
assume any discriminating ability. 

There are also Complex Reflex Actions making use of several nerve- 
arcs, sometimes often forming regular chains of reactions. In these 
cases, the result of one stimulus sets up another, and so on. In fact, 
we call such continued setting up of stimuli reflex chains. As an 
example we may refer back to the frog whose cerebral hemispheres have 
been removed. If we place a fly on the tip of its nose, that stimulus 
sets the "snapping" nerve-arc functioning. Then as the fly is taken into 
the mouth, a new nerve-arc causes a swallowing impulse, which sets up 
reactions of still other nerve-arcs which in turn cause the digestive 
glands to pour out digestive substances. 

It will be noted that such reflexes are quite useful to the animal, 
and it will be remembered that our definition of instinct called attention 
to the protective value of inherited nerve-arc actions. 

Instincts may be deferred. That is, they may not be observable at 
birth, but come forth only later in life when various glands begin to 
pour out secretions which affect many parts of the body. 

It is often stated that instincts are the '"'inherited habits" of the 
individual's ancestors. This was Lamarck's idea. But this cannot be, 

180 General Biology 

because many animals lay their eggs before they themselves have 
developed the later characters, which the offspring possess. Conse- 
quently, the young would have to inherit a habit that the parent was 
going to form later. This is somewhat like saying that because a 
mother is divorced, her daughter inherits a desire for divorce from her 
mother, which, therefore, resulted in the daughter also obtaining a 

While instincts are made up of reflexes, the reflex proper is said 
to affect only one part of the organism, while instinct affects the entire 
body. That is, we should say the winking of the eye, when danger 
threatens, is reflex, while running away from the danger is instinctive. 

Instincts really consist of inner driving forces which make the ani- 
mal possessing them restless until the instinctive act is performed. 
However, we must remember here also that just as with the impulses 
already mentioned, there may be conflicting instincts. In such cases the 
stronger will come forth. Or both may be equally strong, so that no 
action at all will take place. 

Recent psychology often speaks of tropisms. 1 As we have seen from 
our study of former chapters, a tropism is a movement of some kind on 
the part of a living organism. Those who wish to interpret all action 
of living organisms in terms of physics and chemistry are fond of using 
this term. Such men prefer to cast the term "instinct" to the four winds 
of heaven and explain everything in physico-chemical terms. They 
insist that a caterpillar climbs to the end of a twig on account of the 
chemical change in its body that is caused by hunger, let us say. New 
chemical molecules and adjustments are forming, and this makes one 
part of the body lighter than another, so that the laws of physics enter 
and the heavier part will be followed by the lighter in going downward, 
or a chemical affinity of some nature will draw the chemical substance 
of the animal toward it. After having eaten the tiny bud on the twig, 
a new chemical change takes place and so the animal must, whether 
it will or not, obey the next chemical and physical change and descend 
from the twig. 

Dr. Vernon Kellogg, recently in this connection, called attention 
to a scientific friend who explained to Dr. Kellogg that the reason he 
took a corner seat in a restaurant was due to a primeval impulse which 
made him want to have his body in close contact with the wall. But, 
as Dr. Kellogg says, the reason he chose that particular seat was because 
he had made an appointment to meet a friend there. 

As the principal test of an animal's mental ability is the rapidity with 
which it learns, we must know what learning means. Learning means 
the ability on the part of a living organism to vary its actions according 
to some definite plan which will show that it has profited by past 

1 Tropisms really mean growth reactions and taxis mean movement, but most writers use tropism 
to include taxis. 

Animal Psychology 181 

In this connection one is also confronted with difficulties as in 
other fields. Suppose one is attempting to see whether an animal can 
distinguish between colors and then learn to go toward one hue rather 
than another. Suppose now, that the ainmal does not show any more 
inclination of going toward one color than toward another. This by no 
means proves that the animal cannot distinguish, or is unable to learn, 
that there are two colors. It may mean nothing more than that colors 
make so little difference to the animal that there is no reason (motive) 
for his choosing one rather than the other. In such an instance the 
animal's reaction to both colors would be identical, and one could prove 
little or nothing from its behavior. 

Another animal may be thought unable to learn because it tries a 
problem a few times and then ceases to react at all to the stimulus. This 
may be due entirely to fatigue on the part of the organs used, and not 
to inability to learn. That is, the nerve receptors may become dulled 
or tired by new stimuli which are foreign to the animal in its native 

Or again, some sensation may be pleasant to an animal only if 
secondary factors are present, such as the taking of food only when it 
is hungry or when the body is in good health. But surely the rejection 
of food does not mean that the animal either can or cannot discriminate 
between foods. We often will not eat one kind of food, while another 
is relished, or we often will just as readily eat ice cream, candy, or fruit, 
and show just as much desire for the one as for the other; but this 
certainly does not mean that we do not know the difference between 
these three types of edibles. 

Then, too, the state of health makes a tremendous difference in 
what an animal will choose. Dogs and cats eat certain plants at certain 
times, but at other times they will not touch these foods. But do they 
not know the difference between these plants and other food? 

Then, too, an animal may be trained to do certain things, but suppose 
it does these things without having been trained. Can one not argue 
as well that the animal merely stumbled upon doing the act, and then 
doing it often, the nerve-arcs became fixed and the animal can no longer 
help itself? It is now a habit. 

Habits are but acts performed by fixed nerve-arcs. 

The question may arise as to what difference there would be between 
psychology and physiology if all we are to study consists of nerves and 
reactions. Really, there would be no difference in content of the two 
sciences, the difference would consist in emphasis. The psychologist 
lays stress on emotions, feelings, etc., and the physiologist on the simple 
observable reaction which follow a given stimulus. The psychologist, 
in other words, wants to know how the animal feels and what it has 
in its consciousness when a stimulus is applied and its actions are 

182 General Biology 

We have seen in our study of past chapters that the unicellular 
Paramoecium has only two simple reactions, namely, a backward and 
forward movement, while the vertebrate frog can move in many and 
varying ways in order to get out of harm's way. Probably all animals 
can learn. That is, they can be taught to make some change in their 
behavior, but the rate of speed with which they can learn probably 
becomes greater as we ascend from lower to higher phyla. The same 
may be said of the complexity of the problems to be learned. 

When left to themselves, all animals and children learn whatever 
they do learn by what is called the trial-and-error method. This simply 
means that they try something and, if this something is unpleasant or 
painful, they try something else. Contrariwise, if a reaction produces 
pleasure, it is done again and again until it becomes a habit. 

All learning, no matter what it may be, must, however, be based 
on instinct in its widest sense. That is, the problem presented must 
be something which can be solved by making use of some instinctive 
behavior of the animal upon which we wish to experiment. For example, 
a cat can be placed in a closed box in which there is a lever, which, 
when pressed, will open a door. Now, cats are excitable and, when 
excited, will begin to leap about. This is an instinctive action. If, while 
leaping about, the animal strikes the lever and the door opens, it can 
be trained, by enclosing it often enough in the same or a similar box, to 
press the lever without going through the leaping first. 

Learning, then, really means profiting by past experience. But no 
profiting by past experience is possible unless such past experience is 
remembered. Now, such memory by no means must be a definite 
thinking out of a past event and then sitting back and saying "I will" 
or "I will not do this again." Most physical experiences, even in man, 
are merely non-conscious functioning of nerve-arcs. Neither men nor 
the lower animals do any thinking in regard to these simple or complex- 
chain-reflex actions. It is a mere association of one stimulus starting 
another and is called, as already stated, sensory, or associative memory. 

There may, or may not, be an awareness of doing an act, plus an 
associated pleasure or pain sensation. That is, there may be conscious- 
ness not only of the fact that an act is being performed, but there may 
also be an awareness of pleasure and pain, accompanying it, though 
there is little proof that a definite thought — that is, reasoning — is per- 
formed, and that it is then due to such reasoning that changes of action 
are made. These learning acts are in all probability due only to sensory 
memory. ■ 

An example comes to mind. We have all heard some one tell of 
a horse that knows when Sunday comes, that being the only day when 
the animal does not come out of the stable to be harnessed as soon as 
its master appears. 

But does this show that the horse can count up to seven and has 

Animal Psychology 183 

a sort of mental calendar on which he checks off the days? By no 
means ! All it may mean is that if a horse works six days in the week, 
there is a certain feeling of tiredness which has become associated with 
that amount of work, just as a blind man can tell by his "feeling" how 
many blocks he walked and when it is time to turn without counting 
the blocks. 

We may then conclude that all animals may be conscious to some 
extent ; that is, they may be aware of their actions, although this has 
nothing to do with reasoning — with thinking. 

That veteran experimental psychologist, the late Professor William 
Wundt, said, "Animals never think and human but seldom," and most 
animal psychologists hold to this dictum, if, by "reason" is meant true 
thinking, that is, a weighing of two or more sides of a problem and then 
by a definite mental act coming to a decision or conclusion as to what 
is to be done. In other words, thinking means to use abstract ideas and 
to form conclusions. 

There are many writers who mean by the term "thinking" only an 
ability to profit by past experience, so we must always find what a 
writer means by his terms before we attempt to pass judgment on what 
he says. Others likewise speak of "intelligence", which should mean 
only the ability to think, as any associative memory. This is really 
placing old labels on new bottles and is very confusing to the student 
who wishes to know both the past and the present of a branch of science. 

The desires of the different men in animal psychology must also be 
taken into consideration when reading their respective works. There 
are those who wish to show that there is no real difference between man 
and the lower animals. These insist that man has nothing distinct from 
the lower animals except an articulate language, but that man's seeming 
difference in the mental world is only a little greater development of 
animal characteristics. Language by them is often said to be the cause 
of man's greater mental ability in that he can by this means write down 
his findings so that others may profit by them. 

Those who hold that man is something separate and distinct from 
the animal, call attention to the fact that language but expresses 
thought, and one must have thought before he can develop a language, 
rather than language being the cause of thought. These men also insist 
that there is no proof that any animal has ever "reasoned" out a problem 
in the way mentioned in an earlier paragraph, and therefore no animal 
lower than man can be said to have any "intelligence" in the classic 

These latter men would say that hundreds of thousands of cats, 
dogs, and even apes (which are considered the more intelligent animals) 
are very fond of warm places. Such animals have lain before hundreds 
of thousands of open fires and enjoyed the warmth. They have seen 
their masters keep the fire aglow by placing fuel upon it, and yet not 
in a single instance has any animal drawn the very simple conclusion 

184 General Biology 

that it is the fuel which keeps the fire going, and has, therefore, placed 
(without being taught), a single stick of wood on the dying embers. 

Not only this, but the child, when it grows up, teaches others, and 
our schools and colleges are all arranged for the sole purpose of making 
a young man and woman at an early age know what it would take a 
very old person centuries to learn by personal experience. No animal 
is known to teach another a trick which it itself has learned from a 
third individual, unless, of course, the act is instinctive and would have 
been learned anyway. 

Whether one thinks of man as but a more highly developed lower 
animal, or whether one looks at man as a being apart, all agree that 
man can reason, whether he often does or not. All agree that man has 
larger brain-hemispheres of finer texture than organisms on a lower 
scale ; that he has an upright posture and a more delicate hand ; that 
he can use tools, and has the foresight to be able to raise his own food 
and to live in cold climes by understanding the use of fire ; and above 
all, that he is set apart from other creatures not only in having an articu- 
late language, but also in having a knowledge of what he should and 
should not do — in other words, that he has a moral sense. 

So, too, all are agreed that the trial-and-error method of learning 
shows infantile, or animal, intelligence and not human intelligence. All 
education, all colleges and universities have been brought into existence 
to present principles, that is, to present a mental and cultural gauge, 
so that each individual need not try out every detail of experience for 
himself; but, that he can, by learning the principles and laws which 
govern nature, sit back and "figure out" or "reason out" whether a given 
conclusion can or cannot be true. 

This comparison is just as workable in the political and religious 
world as it is in the scientific. Here is shown the difference between 
the educated and the uneducated man. One must not feel hurt or sur- 
prised if an educated man, knowing his principles and his laws, laughs 
at one who proposes a problem or a solution of a problem which can 
immediately be seen to be erroneous. The uneducated man cannot 
understand or see this until it has been tried and found unworkable. 

From what has been said in this chapter we must, if we wish to be 
sure that we are right, know what a writer means by his terms ; we 
must be sure that we are not reading too much of our own thoughts 
into an animal's acts ; we must be sure that we are consistent in our 
interpretations and that, if we explain an animal's behavior in terms of 
tropisms, we must also interpret man's in much the same way; we must 
insist that the observer who is attempting to convince us that his theories 
are correct, has a scientific training and can justly weigh all matters 
that make a distinguishing difference in our interpretations. That is, he 
must be able to separate fact from inference. We must insist that he 
be intimately acquainted with the habits of the animal he is discussing, 
so that he will not assume, for example, that an animal, like many 

Animal Psychology 185 

insects, which have an instinctive impulse to cover up obstructions, is 
showing great intelligence when it covers up a minute stream and thus 
forms a bridge and crosses it. We must insist that he know the past 
experience of the particular animal he is discussing so that he will not 
confuse an associative memory with true intelligence. We must insist 
that he has no personal affection for the animal and thus wants to make 
it "show up" well. And lastly, we must insist that he do not let his 
desire to tell a good story gloss over important details and leave out 

References : 

John Watson, "Behavior an Introduction to Comparative Psy- 

M. F. Washburn, "The Animal Mind." 

S. J. Holmes, "The Evolution of Animal Intelligence." 

Eric Wasmann, "Instinct and Intelligence." 

Vernon L. Kellogg, "Mind and Heredity." 

R. J. A. Berry, "Brain and Mind." 

C. Judson Herrick, "Brains of Rats and Men." 



ONE of the interesting findings of Biology is that it is sometimes 
impossible to determine whether certain types of lower forms 
are plants or animals. The classic example of this is the plant- 
animal Haematococcus consisting of a single cell which moves about by 
means of flagella. 

It will be remembered that Euglena viridis has chlorophyl in the 
body but is classified as an animal. One of the great and outstanding 
characteristics of plants is that most of them possess chlorophyl if they 
grow in the light, and that they are capable of manufacturing their own 
food by virtue of this fact. (See Chapter on the Chemistry of Living 

Pleurococcus (Fig. 85), commonly 
studied in the laboratory, is a close rela- 
tive of Haematococcus. It is a one-celled 
organism found commonly on the north 
side of trees, moist rocks, and wooden 
fences, dull green in color, and powdery 
when dry. When moist it becomes 
brighter in color and slimy to the touch. 
It is found in practically every part of the 
world on the shady and moist sides of the 
objects mentioned above. 

Under the microscope it is found 
that this substance consists of thousands 
of tiny single-celled organisms to which 
the name of Pleurococcus has been given. There is a definite cell wall 
and a nucleus. The chloroplast, however, obstructs a view of the nucleus 
in the unprepared cell. The organism reproduces by simple fission and 
has a tendency to form clusters or colonies, usually of from two to ten 
or twelve cells. When this occurs, the cells assume a more or less 
irregular shape due to the pressure of the adjoining cells. The nucleus 
lies near the center of the cell and contains one or more nucleoli. The 
network of the nucleus can also be distinguished. 

In the cytoplasm will be found the chlorophyl-bearing organ or 
region called the chloroplast. Due to the chlorophyl this will appear 
bright green, but, if the cell be placed in alcohol, the chlorophyl will be 
dissolved, leaving the chloroplast grayish. It is important to note the 
distinction between the chloroplast, which is a living organ of the proto- 

Fig. 85. 

A. Pleurococcus. 

B and C. Haematococcus Cells. 
(Greatly magnified.) 

Intermediate Organisms 187 

plasm, and the chlorophyl, which is simply the green pigment contained 
in the chloroplast. 


In the final analysis, every particle of food, which an animal eats, 
must come from and through the plant world. For example, when one 
eats a piece of steak, the animal from which it was taken, lived either 
directly on plants or on other animals which fed on plant-life. 

Here it is well to appreciate the interesting way nature has of 
keeping a sort of balanced quantity of all needed organisms ; for the 
meat-eating animals or carnivores do not allow an overproduction of 
plant-eating animals or herbivores, and are prevented from multiplying 
too rapidly by parasites in their own ranks ; while much of the vegetable 
world is saved because animals eat each other. 

Consideration of these facts has led to the statement that the 
important thing in life is to get enough to eat and to prevent one's self 
from being eaten. 

The plants manufacture their own food from the substances they 
can extract from the surrounding soil and the air. Plants are, therefore, 
not dependent upon other animals or plants for their food as animals 
are. Those organisms, dependent upon other living organisms for their 
food, are said to be heterotrophic ( ) in nutrition, 

while those, which can manufacture their own food, are said to be 
autotrophic ( ) in nutrition. 

But only those plants, which possess chlorophyl, are autotrophic. 
Therefore, fungi, molds, and most bacteria, which are plants, but which 
have no chlorophyl, are heterotrophic; and, being obliged to live upon 
other organisms, they are parasitic ( ) or 

saprophytic ( ). 

Chlorophyl is either contained in a chloroplast, as already stated, 
or, it is scattered throughout the protoplasm in the simpler green plants. 
Chemically, chlorophyl is a complex compound of carbon, hydrogen, 
oxygen, nitrogen, and magnesium ; its probable empirical formula is 
given by one investigator as C 54 H 72 6 N 4 Mg. Iron, while not a con- 
stituent of chlorophyl, is, nevertheless, always present in the chloroplast 
and seems to be essential to chlorophyl formation. Either in solution 
or in the living plant, chlorophyl absorbs part of the light which falls 
upon it. The energy of the light thus absorbed by the chloroplast is the 
active agent which enables the plant to perform its work. As light is 
required, this process goes on only during the day. 

The materials from which carbohydrate food is manufactured by 
green plants are carbon dioxide and water. Carbon dioxide is present 
in the atmosphere in the small but constant concentration of about 3 
parts per 10,000 parts of air, and, therefore, readily available to such 
plants as Pleurococcus. "Water is absorbed directly from the sub- 
stratum through the cell wall into the protoplast. The carbon dioxide 


General Biology 

taken in is dissolved in the water in which it is readily soluble. While 
the exact steps in the process of formation of carbohydrate foods from 
these substances are not yet clear, the essential facts are well established. 
The carbon dioxide and water are partially or completely reduced to 
their elements, which immediately recombine to form a monosaccharide 
sugar (probably dextrose) with the freeing of oxygen. These two 
processes are represented by the reaction 6C0 5 +6H 2 = C 6 H 12 6 +60' 2 . 
The oxygen is given off into the atmosphere through the cell wall. The 
sugar is the primary food of the plant, being the principal material 

used in the synthesis of other 
foods and in the processes of 
metabolism. When it is pro- 
duced in excess of immediate 
requirements, a further re- 
action takes place by which 
some of the water is eliminated 
and the sugar is 'condensed' 
into starch. This reaction is 
n(C 6 H 12 O c ) = (C 6 H l0 ,O 5 )n+ 
n(H 2 0)." 

Starch is deposited in the 
chloroplast as granules, or 
"starch grains," which form a 
reserve food supply for the cell. 
Starch grains soon disappear in 
green plants kept in darkness 
only to reappear after the plant 
has again been in the light for 
a considerable period of time. 
In some plants, as in Vaucheria 
(Fig. 86), the excess food is 
stored in the form of a fat or 
oil, but it is probable that here, 
too, sugar is the first food 

The process by which car- 
bohydrates are manufactured 
in green plants is called photo- 
synthesis. Its essential fea- 
tures may be summarized as 
follows : "The materials used 
are carbon dioxide and water; 
the energy is obtained from 
sunlight absorbed by chlo- 
rophyl; the chloroplast by the 

Fig. 86. 

I. Asexual Reproduction of the Green Felt 


A, formation and discharge of the large, many- 
ciliate zoospore from the terminal sporangium; B, 
the zoospore showing the ciliated surface; C, sec- 
tion through the surface of the zoospore showing the 
pairs of cilia above the nuclei and the layer of plastids 
beneath; D, germination of zoospore; E, young plant 
of Vaucheria, the two filaments having arisen at op- 
posite ends of the zoospore, one having developed an 
organ of attachment or holdfast h; F, a group of 
plastids, the lower in process of division. (A, B, 
after Gotz; C, after Strasburger; D, E, after Sachs.) 

II. Sexual Reproduction of the Green Felt 


A, Vaucheria sessilis; o, oogonium; a, antheridi- 
um; os, the thick-walled oospore, and beside it an 
empty antheridium; B, Vaucheria geminata, a short 
lateral branch developing a cluster of oogonia and a 
later stage with mature oogonia o and empty an- 
theridium a; C, sperms; D, germinating oospore. 
(From Bergen & Davis "Principles of Botany" by 
permission of Ginn & Co., Publishers. C, after 
Woronin; D, after Sachs.) 

Intermediate Organisms 


use of this energy brings about a chemical synthesis of the materials, 
resulting in the freeing of oxygen and the production of a sugar, some 
of which is usually transformed into starch and stored in that form." 

Some mineral substances, such as magnesium and iron, are also 
necessary for the plant to carry on its life-processes. Nitrogen, potas- 
sium, phosphorus, calcium, and sulphur are also required by most plants, 
although it is to be understood that there are very minute quantities of 
these in so simple a plant as Pleurococcus. 

The process, by which proteins and fats are built up, is not known 
in detail, but it is supposed to be due to the action of enzymes. The 
fats occur in Pleurococcus at those times when the plants become dry, 
and are inactive or in a resting condition. At such times little or no 
starch is formed, while fats are present in quantity. 


The Pleurococcus just studied, though a simple single-celled plant, 
is quite complex when compared with a yeast cell. The yeast cell is 
merely a small mass of granular cytoplasm with various vacuoles scat- 
tered about. These vacuoles must not be mistaken for nuclei. Often 
there are little buds (Fig. 87) on the side where a new cell is forming, 

Fig. 87. 

n, Nucleus; i 

Yeast Cells, 
vacuole; s, ascus. 

Fig. 88. Various Forms of Bacteria. 

a, Spirillum; b, Bacillus typhosus; c, 
Staphylococcus ; d, e, j, h, Micrococcus ; f, k, I, 
Bacillus; g, Psuedomonas pycocyanea; i, strep- 
tococcus. (From G. Stuart Gager's "Fundamen- 
tals of Botany," by permission of P. Blakis- 
ton's Sons & Co., Publishers.) 

and sometimes three or four cells will form within a single wall, in 
which case the outer wall forms an ascus ( ), 

and the cells contained therein are ascospores. 

The nucleus may be shown by special staining processes. 

Yeasts have been called organized ferments because fermentation is 
actually associated with the life of the yeast-cell. That is, there are 
enzymes within the cell (intracellular) which act through the living, 
protoplasm which produced them. They are not poured out as in the 
saliva or the pepsin (extracellular). 

This power of producing fermentation, possessed by yeasts, is still 
retained even though the plant itself be killed with alcohol, ether, or 
acetone So. too, the bacteria, which cause lactic acid in milk, may be 
apparently killed, thus losing their power to perform any of the normal 

190 General Biology 

vital actions such as growing and dividing, and yet be able to produce 
lactic acid. 

Yeast reproduces by budding, also called gemmation ( ). 

A valuable study by the great French bacteriologist, Louis Pasteur, 
has shown that various inorganic substances could be made into a fluid, 
and, if yeast cells were placed therein, they could utilize it for growth 
and reproductive purposes. This ability to use and manufacture new 
substances from wholly inorganic matter sets the yeasts apart as being 
a sort of intermediate grouping between even the lowest plants and the 
inorganic world. 

Yeasts must have oxygen, however, to carry on their work. The 
anaerobic ( ) bacteria are the only exception among 

living organisms in not needing oxygen. 

It must be remembered that the yeast cell is an organism and is 
already existent, only making use of these inorganic substances by con- 
verting them into proteins and carbohydrates, by virtue of the chemical 
enzymes within the yeast cell itself. 

Yeasts work at temperatures from 9° to 60° C. When fermentation 
takes place, as in bread, the temperature is raised during the fermenta- 
tion process by the release of energy. 

Yeast secretes an enzyme which is a sugar ferment. This enzyme 
may, for example, convert starch into sugar, although yeast "utilizes 
only about one per cent of the sugar, and decomposes the remainder into 
carbon dioxide and alcohol. The reaction of the fermentative decompo- 
sition may be expressed as follows : 

Sugar Alcohol Carbon dioxide 

C 6 H 12 0. 6 = 2C 2 H e O + 2C0 2 

It is the production of these two by-products that makes yeast 
commercially important. Yeast produces the same reaction in the sugars 
of cider and wines, and in the metamorphosed starches of the cereal 
grains, which are chiefly used in industry in the production of alcohol. 
The carbon dioxide is also utilized in the making of bread. Yeast is 
mixed with the dough, and, fermenting in it, evolves the carbon dioxide 
gas, which "raises" it, making it porous and improving its digestibility 
and flavor. 

An interesting experiment may be performed by placing a little 
fresh yeast in a bottle of Pasteur's solution (or even in a 15 per cent 
sugar solution made with tap water which will be likely to contain 
enough of the mineral salts for considerable growth). Keep this in a 
moderately warm place. Within twenty-four hours abundant growth 
will be evidenced by the increasing turbidity of the liquid, and by the 
taste of the alcohol in it as well as by the odor of the escaping carbon 
dioxide 1 arising from it. 

*A simple chemical test of the presence of C0 2 in the escaping gas may be made by thrusting a 
glass rod with a drop of lime water suspended on it into the mouth of the culture bottle. The calcium 
oxide (CaO), of which lime water is a solution, readily unites with free carbon dioxide to form a 
white precipitate of calcium carbonate CaC0 3 (CaO+CO.,— CaC3 3 ) which may be seen to form 
in the drop. 

Intermediate Organisms 191 


It is common to hear discussions regarding germs of various kinds. 
Such discussions usually pertain to all those plants and animals which 
are likely to cause disease. Bacteria, however, refer to very minute 
plant organisms classified under the chlorophyl-less fungi (mycetes), 
under the general grouping of schizomycetes ( ). 

While most diseases are probably due to, or associated with, bac- 
teria, very few bacteria, relatively speaking, cause disease. The great 
majority of them are of undoubted value to other' living organisms. 

There are three general shapes after which bacteria are named. The 
bacillus is rod-shaped (b, f, k, 1, Fig. 88), the coccus (c, d, e, f, h, Fig. 
88), (sometimes micrococcus), is berry-shaped or spherical, and the 
spirillum is spiral-shaped or merely curved, something like a comma 
(A, Fig. 88). Bacteria may be so small that only many thousands 
together form a spot sufficiently large to be seen under a high power 
microscope, or they may be of relatively large size. That is, they vary 
from less than 1 micron (the measurement used in microscopy, meaning 
1-1000 of a millimeter, or 1-25000 part of an inch) to 30 or 40 microns. 
It has been estimated (Migula) that there are 1272 distinct species of 

Not only do bacteria vary according to shape, but as to their method 
of growth under varying conditions of temperature and surrounding 

Bacteria may possess cilia or flagella and move quite rapidly. They 
reproduce by simple binary fission. The spirillum and bacillus divide at 
right angles, usually lengthening slightly before division. Cocci may 
divide in different planes, and various names have been assigned to them 
on this account. If they divide into two parts but remain attached, they 
are called diplococci ( ). If they continue dividing 

in one plane but remain attached so as to form chains, they are called 
streptococci ( ). If they divide in two planes. 



:::: * 

• It* 

,jl t^' v J' 

/' %* &?- i\f 

Fig. 89. Various Groupings of Spherical Forms of Bacteria. 

a, Tendency to lancet-shape; b, coffee-bean shape; c, in packets (sar- 
cina) ; d, in tetrads; e, in chains (streptococcus); /, in irregular masses 
(staphylococcus). Magnified 1000 diameters. (After Fliigge.) 

192 General Biology 

they are called staphylococci ( ) ; and if in three, 

sarcina ( ). (Fig. 89.) 

Sometimes the protoplasm of bacteria breaks up into a number of 
bodies within the cell. These bodies are called endospores ( ). 

The value of this breaking up is supposed to be similar to that of 
encysted amoeba ; namely, to permit the organisms to await some more 
favorable feeding period and environment. During this spore state 
bacteria are very resistant. 

The sterilization of various substances in the laboratory takes 
sporulation into consideration, so that when a substance is to be steril- 
ized, it is placed in a temperature of 50 or 60 degrees C. for several days 
in succession, rather than at a higher temperature at one time. This 
permits the spores to germinate. As spores are hard to kill while in 
the spore-state, but readily succumb when placed in a 50 or 60 degrees 
C. temperature after germination, it will be seen that this intermittent 
sterilization is the best method so far known. 

Fischer has divided bacteria into three groups, according to the 
nature of their metabolism: "(1) Bacteria which are like the green 
plants in requiring neither organic carbon nor organic nitrogen. These 
are the so-called prototrophic bacteria, which possess the remarkable 
property of being able to build up both carbohydrates and protein out 
of carbon dioxide and inorganic salts. (2) Bacteria which need organic 
carbon and nitrogenous compounds. These are called the metatrophic 
bacteria. (3) The paratrophic bacteria which live as true parasites and 
can exist only within the living tissue. This group cannot manufacture 
its own food and is like other animals in this respect. The metabolism 
of bacteria may then show all of the phases already described for green 
plant cells and for animal cells as well as certain additional phases. 
The food is absorbed directly through the cell wall and is as varied as 
is their habitat. There seems to be no form of organic substance living 
or dead that may not serve as a source of food supply for bacteria, so 
that the enumeration of their foods becomes practically impossible. A 
special phase of the metabolism of bacteria is illustrated in their relation 
to nitrogen compounds. Nitrogen in an uncombined state cannot be 
used as food energy by most plants. It is obvious that the amount of 
ammonia, nitrites, and nitrates would soon become exhausted unless 
there were some way of supplying more of the nitrogen compounds. 
Many of the soil bacteria are prototrophic in habit and carry on the 
important work of combining the free nitrogen into a form that can be 
used by other organisms. The several nitrogen combinations are effected 
through the agency of several kinds of bacteria. There are also bacteria 
which live in the roots of certain plants, like clover, beans, and peas, 
which are able to utilize the nitrogen of the air. All of the higher forms 
of plants and all of the animals are dependent upon microscopic bacteria 
for their nitrogen. It would be very strange if the character of meta- 
bolism which is so fundamental in living things should be essentially 

Intermediate Organisms 


different in bacteria ; it probably is not, and so the usual steps in 
assimilation and dissemilation may be assumed to take place in bacteria. 
During this process enzymes are utilized and toxins produced." 

Bacteria increase with marvelous rapidity by becoming- larger in 
size, followed by a division of each organism into two. If each of these 
divide every half hour, a single bacterium will have become something 
like 17,000,000 individuals in twenty-four hours. It can be seen quite 
readily that such a tremendous increase in so short a time means that 
vast quantities of food must be at the bacteria's disposal, or the organ- 
isms themselves must die. If they are then in the body of an animal, 
the effects of the poisons produced by their dead bodies may be an 

important factor in injuring the host. 

However, comparatively few types of 
bacteria are pathogenic. Most of them 
have some useful function. They are the 
chief agency in decomposition and decay 
by which they help to restore organic 
materials into the general circulation of 
nature's economy. 

Bacteria spoil food and rot substances 
which then become soil fertilizers; they 
sour milk and ripen cheese; they break 
down tissues in disease, and aid in diges- 
tion. They do much that makes life in the 
higher organisms possible, while at the 
same time doing many things which cut that life short. 

While it was only after microscopes were invented that bacteriology 
could become a science, still it has always been known that acid solutions 
and salt solutions keep food from spoiling and that heavy sugar solu- 
tions do the same. Thus it was possible to pickle and preserve foods 
and to make jellies. 

Bacteria require heat and moisture for their growth, so that fruit 
and meats can be dried. By preventing one of the important factors 
for bacterial life from being available, such meat can be preserved for 
great periods. 

Drugs and chemicals which prevent the growth of bacteria are 
known as antiseptics. Thus, the ancients poured wine on wounds as an 
antiseptic. We use alcohol to-day instead of wine. 

In agriculture there are certain soil-bacteria which produce tiny- 
galls ( ), commonly known as tubercles (Fig. 90), 
on the roots of clover and other leguminous ( ) 
plants. These serve a very important purpose in that they derive nitro- 
gen directly from the air and supply it to the clover. This makes it 
possible for clover to grow in soil very poor in nitrogen, while the over- 

90. Tubercles (Galls) on the 
Roots of Red Clover. 

1, section of ascending branches; 
b, enlarged base of stem; t, root- 
tubercles containing bacteria. 

194 General Biology 

possible for clover to grow in soil very poor in nitrogen, while the over- 
production of nitrogen leaves the soil richer than it was before. 

The galls themselves are filled with rather large x- and y-shaped 
bacteria, easily seen under the microscope. These bacteria die, and 
the nitrogen which they contain is added to the surrounding soil, some- 
times directly, and sometimes through the intermediate plant to which 
it is attached. 



WHETHER the study of Biology be taken up by those who intend 
to practice medicine, or for general cultural purposes, the fact 
remains that all of us, at some time in our lives, require the 
services of a medical man. Likewise, all of us, who make any pretense 
whatever at being college men and women, feel, and rightfully so, that 
unless we can intelligently follow at least ordinary scientific articles in 
the various magazines and journals published for educated men and 
women, there has been some radical defect in our instruction. 

Practically all modern medicine is based upon the theory of 
immunity, and neither the medical man, the medical student, nor the 
educated man at large, can intelligently discuss or intelligently under- 
stand anything that may be told him regarding himself or the method 
of treatment suggested when disease comes to him, unless the theory 
of immunity is understood. 

The subject of immunity is rather difficult. It is, in fact, probably 
one of the most difficult which confronts the first and second year student 
of Biology; but his ability to grasp and understand the theory is, in a 
way, a test of his ability at understanding and applying the knowledge 
he has gained in Biology. 

All coelomates have their bodies arranged as one tube lying within 
another, and, if one could draw out any coelomate body lengthwise, 
the outer part would appear as a tube with very thick walls, while the 
gastro-intestinal-tract would form an opening through the entire body. 
In fact, the whole body would appear quite similar to an ordinary thick- 
ened gas pipe (Fig. 164). 

One can readily understand that*the opening in the gas pipe is really 
subject to the same atmospheric and environmental conditions that the 
outside of the pipe may be. So, too, the intestinal tract, with all its 
diverticula, is really outside of the body in so far as the atmospheric 
surroundings are concerned. In fact, the interior portion of the gastro- 
intesinal-tract is just as much outside the body (although not quite as 
much exposed) as is the skin on the outer surface. 

Now, the surface on the inner side of the gastro-intestinal-tract, just 
as the skin, forms a layer which can, under certain conditions, be pene- 
trated by either physical, chemical, or living substances. We know that 
we can scratch or cut ourselves. This results in a physical injury. We 
know that poisons are chemicals which can injure tissues whenever 
such poisons get into the system, and we also know that living organ- 
isms, such as bacteria (unicellular organisms from the plant worlci) and 

196 General Biology 

protozoa (unicellular organisms from the animal world), can take up a 
sort of parasitic life within other living forms. Whether a given sub- 
stance injures chemically, or whether a living organism is to find its 
way into another and injure it, depends upon whether or not the foreign 
substance or organism can penetrate through the outer skin-surface of 
the body or through the surface of the gastro-intestinal-tract. It is only 
when such foreign objects are able to get within the body proper (that 
is, within the space between body surface and intestinal surface) that 
injury results. 

Probably most of such injurious substances are taken in through 
the mouth and later find their way through the more or less delicate 
lining of the gastro-intestinal-tract. It is of value to note that the 
severity of a burn, in the area affected, depends upon the length of time 
the particular area remains in contact with either fire or acid. This 
means that a deep or severe burn in a localized area may cause death, 
while a less severe burn spread over a greater area may not. 

Now, if a liquid, which can neutralize or wash away the given 
substance, could be thrown upon the acid at the time it is spilled, such 
acid would be washed away immediately, and little, if any, harm would 
be done. So, too, in the gastro-intestinal-tract, an injurious substance 
which may find its way therein, may be neutralized or washed away if a 
sufficient quantity of neutralizing fluid is secreted or passed through the 
intestinal tract. 

Therefore, two things must be kept in mind when discussing a 
subject of this kind: the strength or power of the injuring agent, and 
the length of time the injuring agent remains in contact with a sus- 
ceptible surface. In fact, one may add a third factor, for there is a 
possibility of a foreign substance being taken into the system which 
may so affect the regenerative abilities of the host, as not only to prevent 
healing of a wound, but which will actually continue to irritate and 
injure more than the original injuring agent. 

Once the injuring agent has entered the body, the question arises 
as to the method by which it injures the host. It must be remembered 
that living organisms, whether they be bacteria or protozoa, are in turn 
subject to the same laws which govern the life of the host itself. Some 
of the larger parasites, such as tapeworms, really remain within the 
intestinal tract and use the food of the host before the host himself 
derives the benefit of what he has eaten. There are also parasitic pro- 
tozoans, such as the malarial parasite, which, once it has entered the 
blood stream, actually eats out the center of the blood cells. Then there 
are those which use some part of either the blood or other tissues of the 
body for food and in this way injure the host ; or again, there are those 
which use but a very small quantity of the host's food and are conse- 
quently not particularly injurious to the host on that account; but the 
various excreta ejected by these parasites may prove injurious either as 
a mechanical obstruction of some kind or as a chemical poisoning. And 

Immunity 197 

still again, various poisonous substances may be formed by the parasites 
themselves, which will injure the immediately surrounding tissues of 
the host only in the location of the parasites ; or, the poisons may be 
soluble in the blood stream and in this way pass throughout the entire 
body, injuring many regions. And there is still another way by which 
injury is brought about by parasitical invaders. There are certain 
bacteria and protozoa which require considerable oxygen for their life 
processes. The red blood corpuscles have become red by coming in 
contact with the air in the lungs and absorbing oxygen which they then 
distribute throughout the body. If the parasite, however, takes this 
oxygen from the red blood cells, only carbon dioxide and, under certain 
conditions, carbon monoxide remains. Carbon monoxide is a constitu- 
ent of "coal gas," which often asphyxiates men working in coal mines. 
It, therefore, follows that one actually may be "gassed" and die of this 
"gassing," if the body contains parasites which remove the much-needed 
oxygen from the red blood corpuscles. In such instances where oxygen 
is withdrawn, death results almost immediately. 

Then there may be all manner of mixed infections. Just as it 
requires fire in order to cause powder to explode, so there are certain 
chemical substances, as well as living organisms, which by themselves 
do little harm or injury; but, when a second or third substance mixes 
with them, may prove quite injurious. Conversely, a single substance 
may be quite injurious, such as either an acid or an alkali ; but, when 
the two are mixed, they neutralize each other, and no active injury is 
brought about. 

Everyone knows that no two people are exactly alike in their ability 
to resist disease, and that one person may tolerate a much greater injury 
than another without succumbing to it. Most of us have probably read 
of the ancient king who, being afraid that an enemy might poison him, 
took small doses of various poisons daily so that in due time he could 
take great quantities without its having any injurious effect upon him. 
That is, his toleration for this specific poison grew, and his body was 
able to resist the usual injury caused by such poison. That is, his system 
became insensible to specific poisons which were thus unable to affect 
him injuriously because an immunity to these poisons had been set up. 

Resistance, tolerance, and immunity may be classified in various 
ways, such as racial, familial, and individual. As an example of race 
immunity we have those groups of individuals living in the tropics 
who do not succumb to the various tropical fevers that affect a stranger 
almost immediately. The classic example, however, is that of the Jews, 
who having fought tuberculosis for thousands of years, are now more 
immune than any other known race of mankind. The Negroes and 
Indians, on the contrary, never having had tuberculosis until the white 
man brought it to them, succumb quickly. 

If certain families seem to be more or less immune, we call this a 

198 General Biology 

familial immunity, and if only an individual is intensely resistant to a 
given disease or injury, we speak of it as individual immunity. 

Immunity is also divided into (1) natural immunity (under which 
racial immunity can be classified), and (2) artificial immunity. The 
second of these divisions is again subdivided into active and passive 

Bacteria either contain poisonous substances (endotoxines), as does 
the typhoid fever bacillus, or they produce poisonous substances (merely 
called toxins or ectotoxines) as does the diphtheria bacillus, tetanus 
bacillus, etc. 

Now, if these toxic substances are distributed within the body, the 
body tries to protect itself by manufacturing antitoxins, which are 
opposing substances for the purpose of neutralizing the poisons and thus 
preventing them from injuring the system. If the toxic poisons are not 
too severe, the antitoxin prevents a disease from forming. 

As an example we may cite typhoid fever. Here the antitoxin is 
not only manufactured, but actually remains in the body of the patient 
for some years after the disease has passed away. The great quantity 
of antitoxin present can, during these years, thus prevent another attack 
of the disease if the typhoid bacillus again gets into the body. Such 
an individual is, therefore, during the time the antitoxin is present in his 
body, immune to new attacks of typhoid fever. He is immune because 
his body produced immunizing bodies which protect him. His body is 
active in producing these immunizing bodies, and such immunity is 
therefore called an active immunity. 

An animal which, in a specific disease, also builds up such anti- 
bodies or immunizing bodies, may have these antibodies removed from 
its blood. The liquid part of the blood, which contains the antibodies, 
is called an antibacteriological or antitoxic serum. Such sera are then 
injected into human beings. As the person, into whom they are injected, 
then has protective substances which he does not otherwise have, he 
(without having his own body manufacture the antibodies) becomes 
immune for a certain length of time to the specific disease for which the 
antibodies were manufactured in the animal's body. Such an immunity 
is. therefore, called a passive immunity. 

It is upon principles evolved from these facts that the various 
vaccines have been brought forth against cholera, typhoid fever, small- 
pox, etc., as preventive measures, as well as the therapeutic sera injected 
after the disease is present, as in meningitis, diphtheria, tetanus, etc. 

We know that various chemical substances have definite affinities 
for each other, and, to explain the mechanism of immunity, it is assumed 
that every cell in the body has some particular chemical attachment or 
affinity. Let us say that a certain molecule connected with each cell 
has an affinity for various substances which pass through the body. 
This molecule is called a receptor. We know that normally, as blood 
passes the different cells of the body, the cells have a selective action; 

Immunity 199 

that is, they practically reach out and drink in what they need. One 
of the experiments performed on Paramoecia demonstrates what is 
meant by this chemical selective action. It is there shown that certain 
chemical substances, such as a sugar solution, may cause the animal to 
go in an opposite direction, but, if it has once gone into the solution, 
it will not again leave. This selective action, which all cells probably 
possess to some degree, may work on a similar basis ; that is, normally, 
the molecule (the receptor) draws to itself the particular food that it 
needs as the blood passes. But, just as Paramoecia may actually enter 
the sugar solution or even an injurious solution, so the molecule or 
receptor may also sometimes take or select from the passing blood 
various poisonous or toxic substances and unite them with itself. This, 
of course, injures the cell to which the receptor is attached. 

We know from ordinary observation that, whenever we injure our- 
selves sufficiently, a scar forms. Then, too, it will be noticed that the 
scar is almost always slightly elevated. This means that more scar 
tissue has actually formed than there was skin before. From micro- 
scopic studies we find that, whenever those particular cells known as 
fibroblasts (which form a goodly portion of the connective tissue ele- 
ment of the body) "are injured, they grow much more rapidly and pro- 
fusely than they did before such injury took place ; in other words, if the 
fibroblasts are injured, more connective tissue will grow in the region 
of injury than grew originally. Once an injury takes place and regen- 

Oeration or regrowth begins, there 
I -*-i c: • t00 * *\ * s usually an excess of such re- 

l_ _P P / generation or growth. 

With this in mind it is easy 
cL °* to understand that, when a 

Fig> 91 \ ctSdiS2t y ^ Factors molecule or receptor has anchored 

cl., the cell to be dissolved; c, the com- to itself a poison (Fig. 91) which 

plement or solvent by which it is dissolved; ininrPQ trip pp11 tn whirri trip rp- 

a., the amboceptor or intermediate body by injures tne Ceil IO WniCU tne re- 

which the two can be brought together. ceptor is attached, the cell may 

grow several receptors where it had only one before. Such excessive 
production of receptors causes a portion of the receptors tO' be thrown 
off from the cell. These separated receptors then find their way into 
the blood-stream. The receptors in the blood-stream are able to anchor 
poisons to themselves just as when attached to cells. .This means that 
there are great quantities of these receptors taking up the poison which 
would otherwise injure the various cells with which the poisons might 
come in contact. The receptors thus prevent injury to cells which nor- 
mally would be open to attack. 

Certain conditions, however, must be fulfilled before the receptors 
can unite to themselves the poisonous substance, and the condition 
necessary in this instance is that a certain ferment-like substance, called 

200 General Biology 

a complement (or alexin), be present. These are protectors against 

Complements can be demonstrated to exist in the laboratory. When 
blood serum is placed in a test tube, the receptors do not unite with the 
toxin if a very small amount of heat is applied to the serum proper. 
Heat kills or paralyzes whatever it is that makes the union possible. 
If, however, we add but a very small amount of unheated serum, the 
union takes place almost immediately. Whatever it is that has been 
destroyed by the heating and permits or causes the receptor to unite 
with the poisonous substance, is called the complement. 

It is quite possible that certain cells of the body, or even all the 
cells of some animals, may have no receptors at all for certain poisons, 
and, therefore, such cells and animals would have a natural immunity 
toward those poisons. It is because the thrown-ofT receptor needs the 
complement before it can anchor the poison that it has been called 

The foreign body or substance is called the antigen, while the ambo- 
ceptor produced by the action of injurious antigens is known as the 

It is of great importance to know that the molecule which is the 
amboceptor is decidedly specific. That is, an amboceptor will react only 
to one specific foreign substance, so that antibodies formed in diphtheria, 
for example, will not be the same as those formed in tetanus, nor will 
they be able to assist in anchoring poisons produced in tetanus. 

Quite naturally, the rate and ability of metabolism in a cell will 
determine how rapidly receptors are formed, and consequently will de- 
termine how rapidly immunity can be brought about. This means, in 
turn, that, if the poisons can act more rapidly than the cells, the cells 
as well as the possessor of those cells will succumb. 

The growth, development and action of phagocytes (white blood 
cells which devour foreign substances) are also subject to this same rate 
and ability of metabolism. Some phagocytes may devour a foreign body 
before the latter has time to bring about an injury. 

Some phagocytes may not have within themselves a chemical sub- 
stance which can dissolve the invader, and so the invader may continue 
to live even though engulfed by a phagocyte, or, the invader may even 
kill the phagocyte. 

Then it must be remembered that in all parasitic organisms the 
same conditions largely apply which apply in the host, so that, just as 
the host may strengthen his resistance, so the parasite may strengthen 
its virulence to overcome the increasing resistance of the host. For 
example, about the bodies of the anthrax bacillus and the pneumococcus, 
capsules form which make them more resistant to any injurious sub- 
stances of the host. And these capsules only form in the body of a 
host where some kind of immunity is possible. In cultures in the 

Immunity 201 

laboratory, where no immunity is brought into play, capsules do not 
form on the groups mentioned. 

The encapsulated forms are not subject to phagocytic action, and 
some even continue to produce more and more powerful poisons to 
injure the unlucky phagocyte which may devour it. 

It is assumed that inflammations and fevers probably cause an 
increased production of phagocytes and chemical neutralizations to 
protect the body in injury and disease. 

The amboceptors anchor soluble poisons only when the complement 
is present. 

Similarly, phagocytes will not engulf bacteria unless the bacteria 
have first been prepared for such engulfing by substances in the normal 
blood serum similar to the complement called opsonins. If an animal 
has been immunized already by repeated introductions of bacteria, still 
more resistant bodies called bacteriotropins appear. These bacterio- 
tropins (which are only a sort of outstanding opsonin in immune sera) 
act as opsonins and prepare the bacteria for the phagocytes. Opsonins, 
bacteriotropins, and in fact all substances which prepare foreign sub- 
stances for the phagocytes, are called cytotropins. 

When foreign bodies of any kind dissolve body substances, they are 
said to be cytolytic (kytos-cell+lysis-dissolving) if they dissolve the 
cytoplasm ; haemolytic, if they dissolve the red substance (haema=: 
blood) in the blood cell ; hepatolytic (hepar=liver) if they dissolve liver 
cells, etc., etc. Such lysins are usually antibodies. 

If a reaction can be produced, which will cause bacteria or cells to 
clump together, such clumping is called agglutination, while the sub- 
stances in immune sera which cause agglutination are called agglutinins. 
This is commonly called the Widal reaction. Agglutination is so specific 
that the serum of an individual suffering from typhoid fever, or even 
the serum of one who has had the disease, will cause the clumping 
of typhoid bacilli when a few drops of it are placed in a culture of the 

If any foreign protein substance is injected into any of the higher 
animals, new substances similar to antibodies are formed. These are also 
specific in acting on the same protein substances by causing a cloudy 
precipitate, and sometimes by changing the protein by breaking it up 
into simpler substances, some of which are poisonous. This fact makes 
it possible to tell whether blood stains are those of a human being or not. 
For example, the clear serum of a rabbit can be treated with human 
blood serum and, if even a portion of the dissolved human blood stain is. 
then added, a cloudy precipitate forms, although this precipitate will 
not form when blood from a lower animal is added. Similarly, if the 
rabbit's blood be first treated with the blood of a lower animal, human 
blood will not cause the precipitate. 

A strange phenomenon has also come forth in recent years, known 
as an anaphylactic shock. This is probably connected in some way with 

202 General Biology 

the precipitation reaction. It means that an animal already immunized 
to a protein may die when additional protein of the same kind is injected. 
This condition in an animal is known as anaphylaxis ( ). 

In other words, we may say anaphylaxis is an oversensitiveness of the 
organism toward bacterial toxins and foreign sera. The reason for 
anaphylaxis is not yet satisfactorily explained. 

The principle of anaphylaxis is used to diagnose certain diseases. 
The tuberculin reaction is nothing more nor less than the injection of 
the proteins of the tubercle bacillus into the skin, which (because the 
dose is very small) does not overwhelm the entire nervous system, but 
produces only a fall in temperature and a slight fever, if the disease is 

An antitoxin is, as already stated, the soluble substance produced 
which neutralizes quantitatively fresh injections of the same poison. 
The commercial diphtheric antitoxin is merely the serum of a horse 
which has had repeated doses of diphtheria toxin injected until it has 
been brought into a state of active antitoxic immunity. Like all 
immunizing agents, antitoxins are all specific for some single toxin. 

In this connection it is interesting to note that sheep, while they are 
very susceptible to the toxin formed by the tubercle bacilli, are not 
susceptible to the injection of the dead bacilli themselves. Guinea pigs 
are quite susceptible to the bacilli but not to the toxin. The proteins 
of our own body injected into ourselves are poisonous. 

The various ways in which immunity is produced by injection of 
foreign substances, may be summarized as follows : 

(1) The virulent parasites are administered in small doses so as 
to give the individual the disease in a mild form (active immunity). 

(2) Weakened parasites may be injected in larger doses and pro- 
duce the same result. 

(3) Dead bacteria may be given in place of living, so as to produce 
a feebler but similar result. 

(4) The poisons may be isolated from the parasites, and gradually 
increasing doses injected, thus increasing the normal neutralizing ability 
of an individual. 

(5) Serum from an animal, immunized by one of the above 
processes, may be placed directly into another individual and thus permit 
him to become immune without going through any form of the disease 
himself (passive immunity). 



EVERYONE is already familiar with some of the higher groups of 
plants known as "flowering plants," but everyone is. not familiar 
with the fact that flowering plants are few in number, indeed, 
when compared with the thousands of different kinds of minute plants 
that cannot even be seen with the naked eye, and which do not bear 

Prominent among these latter are such single celled plants as 
Pleurococcus, the yeasts, and bacteria already studied. But there are 
others also, which, though commonly seen, must remain unknown unless 
observed under the microscope. 

To be able to discuss the plant-world intelligently one must know 
certain terms commonly used, just as it was necessary to know the 
various names of the many parts of the frog before the animal-world 
could be intelligently discussed. 

The following outline and drawing (Fig. 92) will give such a knowl- 
edge of terms : 

Plant Body < 

Root (with or without branches) 

Stem (with or without branches) 



Leaves < 



Base of the Blade 


Petiole (the leaf-stalk) 

Stipules. (Small leaf-like structures 
at the base of the petiole.) 

There are as many and varying classifications of plants as there are 
of animals, but, four great groupings hold their own because these group- 
ings are simple and easily understood. 


General Biology 

They are as follows : 

Thallophytes ( 
plant body. These are made up of : 

Algae (Chlorophyl-bearing thallophytes). 

Fungi (Thallophytes without chlorophyl) 

Bryophytes or Moss Plants ( 

Pteridophytes and their allies ( 
and their allies. 

Spermatophytes or seed plants ( 

). Plants possessing a simple 


). The ferns 


Fig. 92. Leaf, Root, 
Shoot and Flower. 

A. Leaf of a wil- 
low (Salix sp.) b., 
blade; p., petiole; s., 

B. Diagram to show 
the essential parts of 
a "flowering" plant. 
t.r., tap-root; b.r., 
branch root; cot., seed- 
leaf (cotyledon) ; *., 
internode; a.L, leaf- 
axil; n., node; a.b., 
axillary bud; r., re- 
ceptacle of floral or- 
gans; ca., calyx; per., 
perianth; co., corolla; 
st., stamens (androe- 
c i u m) ; pi., pistil 

(From C. 
lission of P. 

Stuart Gager's "Fundamentals of Botany," by per- 
Blakiston's Sons & Co., Publishers.) 

Simple Plants 



Thallophytes. These plants have a mere plant body without a true 
stem, roots, or leaves, though there may be parts that resemble stems, 
roots and leaves. They may be very fragile, as are some of the thread- 
like green Spirogyra (Fig. 93), (also called pond-scum and frog- 
spit), commonly found in fresh-water creeks and ponds, or tough sea- 
weeds, like the brown kelp many feet in length. The cells usually grow 
end to end. 


Fig. 93. 

The band-like chloroplasts extend 
in a spiral from one end of the cell 
to the other. In them are imbedded 
nodule-like bodies (pyrenoids), and 
near the center of the cell the 
nucleus is swung by radiating 
strands of cytoplasm. (After Stras- 

. As was seen when living organisms 

were discussed, there are no hard-and-fast 

'hhroplad rules by which one may classify anything. 

There are some Thallophytes which really 

-JVuc/eus have stem-like and leaf-like structures, but 

Pyrenoids the classification originally based on struc- 
tures, must now be thought of more from 
a functional or life-cycle point of view. All 
thallophytes are alike in having a more or 
less simple life-cycle, so this must serve us 
as a basis. 

are red, Rhodophyceae ( 
Myxophyceae ( 
Spirogyra ( 

The various algae (Fig. 94) are named 

after some distinctive characteristic ; thus 

those which are green are called Chloro- 

phyceae ( ) ; those which 

) ; those which are slimy, 

), etc. 

) is in turn a representative of the 

Chlorophyceae. The cells are elongated and attached end to end. There 
are spirally arranged bands (chromatophores or chloroplasts) which 
contain chlorophyl. The number of these bands and the method of 
coiling depend upon the species to which each belongs. The cytoplasm 
is rather thin and lies next to the cell-wall, while fine threads of it 
extend to the nucleus. The special centers in the chloroplasts, where 
starch is stored, are called pyrenoids ( ). Nearly 

98 per cent of the cell is water, yet the two per cent remaining can 
perform every one of the four vital processes. The bubbles often seen 
are filled with oxygen which is a waste product of photosynthesis. 

Reproduction takes place in two ways, either by the individual cell 
dividing at right angles to the length of the cell, or after two individuals 
have conjugated. The latter is seen when two plants lying close together 
send out projections (Fig. 95) which unite, forming bridges through 
which the cytoplasm of one plant mixes with another. In fact, these 
two cells may unite so thoroughly that they become one, becoming 


General Biology 

p j ~ -jp?^ 


Fig. 94. Chlorophycae, Rhodophycae, and Myxophycae. 

A. Cladophora, a branching green alga, a very 
small part of the plant being shown. The branches 
arise at the upper ends of cells, and the cells are 

B. A red alga (Gigartina), showing branching 
habit, and "fruit bodies." 

C. Three common slime moulds (Myxomycetes) 
on decaying wood: To the left above, groups of the 
sessile sporangia of Trichia; to the right above, a 
group of the stalked sporangia of Stemonitis, with 
remnant of old Plasmodium at base; below, groups of 
sporangia of Hemiarcyria, with a Plasmodium mass 
at upper left hand. (A, after Caldwell; B, after 
Schenck; C, after Goldberger.) 

The Union of the Gametes in Spirogyra. 
A, two filaments of Spirogyra quinina, 
side by side, showing stages in the union of 
the cells (gametes) to form the zygospores; 
B, another species (S. longata), in which the 
cell unions occur between adjacent gametes in 
the same filament. (After Schenck.) 

smaller as a thickened wall is 
secreted about it. When this 
latter event takes place, the 
organism is said to be in a 
spore state, and because the 
spore has been formed by the 
fusion of two cells, it is often 
called a zygospore ( ). 

Conjugation is thus a prepara- 
tory process to permit a mix- 
ing of the parent chromatin 
before actual reproduction 
takes place. 

It has already been ex- 
plained that a sexual germ-cell 
is known as a gamete. The 
zygospore is, therefore, now 
one cell, the product of the 
fusion of two gametes. There 
is here, then, the beginning of 
sex-life in the plant-world. 
This is why the two conju- 
gating and fusing parent cells 
are known as gametes. 1 

The spore cannot escape 
from the parent cell, however, 
until such parent-cell decays. 

Artificial Fertilization. — 
Something like a hundred years 

Fig. 96. A Common Foliose Lichen (Parmelia) 

Growing Upon a Board, and Showing 

Apothecia. (After Goldberger.) 

'This is the first sign of two sexes we shall see in the laboratory, although the very first sexual 
differentiation in plants probably lies in the Volvacales (Fig. 97). 

Simple Plants 


Fig. 97. 
Volvox Globator, a Colonial Form of the Volvocacece. 
(See Fig. 49, where this same form is considered an 

A, mature colony, with four daughter colonies devel- 
oping in its interior; B, section of the edge of the colony, 
showing three vegetative cells and a developing egg; 
C, a packet of sperms within the parent cell and a single 
sperm very much magnified at the side; D, an egg sur- 
rounded by a swarm of sperms; E, an oospore with 
heavy protective wall. (From Bergen & Davis' "Princi- 
ples of Botany," by permission of Ginn & Co., Pub- 

ago Spallanzani fertilized 
the eggs of various animals 
artificially, while more re- 
cently several workers have 
succeeded in causing eggs to 
begin to grow by chemical 
means. The experiment was 
first successfully made with 
the eggs of sea-urchins and 
other marine animals by a 
zoologist, Loeb. In 1913, 
Overton successfully accom- 
plished the same thing with 
the eggs of Fucus. The eggs 
were dipped in a mixture of 
50 cc. of sea-water plus 3 cc. 
of a very weak solution of 
acetic, butyric, or other fatty acid, for about a minute, or a minute and 
a half to two minutes, and then transferred to normal sea-water. The 
formation of the fertilization-membrane was caused in this way quite 

as in natural fertilization by the 
sperm. It was also found that, after 
the formation of the membrane, if 
the eggs are placed for 30 minutes 
in hypertonic sea-water (50 cc. of 
normal sea-water plus 8 to 10 cc. of 
a weak solution of sodium chloride 
or potassium chloride), and then 
back into normal sea-water, the 
eggs will begin to divide and con- 
tinue to develop into young plants. 
The chromosome number in the cells 
of plants formed by artificial fertili- 
zation, although a question of very 
great interest, is still unsolved. 

Fig. 99. Phycomycetes. 

These are the alga-like fungi without septa 
in the mycelium, except in the sporing 
branches, where they occur to cut off the spore- 
bearing cells. The septa also occur in old 
filaments. The mycelium is therefore continu- 

Common water mold (Saprolegnia) : A, 
a fly from which mycelial filaments of the par- 
asite are growing; B, tip of branch organized 
as a sporangium; C, sporangium discharging 
biciliate zoospores; F, oogonium with an- 
theridium in contact, the tube having pene- 
trated to the egg; D and E, oogonia with 
several eggs. (A-C after Thuret; D-F after 
De Barry.) 

Fig. 98. Growth Habit of the Bread Mold 
(Rhizopus Nigricans.) 

Sketch showing two groups of erect hyphae 
bearing sporangia, with rootlike clusters of 
filaments at their bases. 


General Biology 

It must be remembered that the egg was already there. Artificial 
fertilization merely hastened a normal action. This does not throw any 
light on the origin of life as it is popularly supposed to do. 


This is the common "green felt" (Fig. 86), usually found on soil, 
although it is often also found in water. The thread-like filaments are 
coarser and longer than spirogyra, and they also branch. Vaucheria are 
tube algae. 

There is an interesting difference here from the spirogyra in that 
there are no transverse cell-walls throughout the entire filament, but 
many nuclei are scattered about. Such a form is called a coenocyte 
( ) or syncytium (I. E., Fig. 86). 

Fig. 100. Ascomycetes (Sac-like Fungi). 

The figure shows the characteristic group- 
ing of asci. The layer in which the asci ap- 
pear is called a hymenium. In these the 
mycelium has dividing septae and the spores 
are contained in asci. (After Chamberlain.) 

Fig. 101. Basidiomycetes. 

Typical basidium with sterigmata (distal 
short stalks), showing spores in different 
stages of development. (After De Barry.) 

In basidiomycetes the spores develop on 
little club-shaped hyphae. Smuts, rusts and 
mushrooms belong in this group. 

Reproduction takes place both sexually and asexually (Fig. 86). In 
the latter case the old end of the filament dies, setting free the branches 
which become separate plants, or a cross wall forms in one of the 
branches. A thickening occurs beyond this cross wall, and this thick- 
ening is known as a zoospore. The zoospore breaks away from the 
parent plant, swimming about for a time, and then becomes a new 

It is made up of many cells but forms only one plant. 

Simple Plants 209 

Sexual reproduction occurs when one or more large oval protrusions 
form on branches which have grown out apparently for this purpose. 
At the very end of this branch is the terminal cell in which many small 
cells are formed. These small cells escape into the water. Each one 
possesses long cilia by means of which it swims about. A single one 
of these ciliated forms enters the oval mass. The little ciliated form 
is known as the male gamete, and the large oval protrusion as the 
female gamete. The organ which produces a gamete is called a gonad 1 
( ). The oval body is consequently known as an 

oogonium ( ) or egg-gonad. Two gametes, uniting 

as have the two just mentioned, form a single cell known as an oospore. 
This oospore, after a short period of rest, forms a new plant. It will 
be noted that in vaucheria the gametes are of unequal size. In spirogyra 
they were of equal size. In fact, whenever gametes are formed, it is 
the smaller and more active one, regardless of whether there are any 
other distinguishing features or characteristics, which is called the male 
gamete or sperm, while the larger and more passive one is known as the 
female gamete or egg. 

The union of sperm and egg is called the process of fertilization. 

The male gonad is called the antheridium ( ), 

and the female gonad is known as an oogonium. 

Some algae live with various fungi. These symbiotic ( ) 

plants are the lichens ( ) (Fig. 96). 


The Algae-like, or tube fungi, make up the Phycomycetes, while the 
higher fungi, such as mushrooms, toad-stools, puff-balls, rusts, and smuts, 
are known as Carpomycetes. 

The fungi, no matter how differently they may appear or in what 
out-of-the-ordinary place they may grow, are alike in two great char- 
acteristics : 1. They possess no chlorophyl, and 2. They reproduce by 

They live either upon decaying matter, in which case they are called 
saprophytes, or at the expense of another organism when they are called 

Bread Mold is easily obtainable, but that from fruits or from dead 
flies serves just as well for study (Fig. 98). There is a tangled mass 
of thread-like structure which is the working body of the plant. This 
tangled mass is known as mycelium ( ), while the 

individual threads are known as hyphae ( ). If the hyphae 

send out threads in turn, these are called rhizoids ( ), 

and these little root-hairs penetrate the substance on which the mold 
forms and through which it absorbs what is needed. It is supposed 

1 Botanists do not look with favor on the term "gonad" in plants, but it has seemed advisable 
to use this term here, for, in zoology the student must use it constantly. 

210 General Biology 

that enzymes are produced in the hyphae which can make the bread or 
fruit utilizable to the plant. 

Reproduction takes place by a number of upright stalks, called 
sporangiophores ( ), growing from the mycelium. 

There is formed a spore-case, or sporangium, at the very tip of the stalk. 
In this the spores are formed and, when the spore-case bursts, the dust- 
like particles, which are really spores, are scattered about by air currents. 

There may be sexual reproduction in the molds quite similar to that 
in Spirogyra. Two hyphae unite by their free ends and a wall forms, 
thus producing two end cells which eventually become a single spore 
with a very dark heavy wall. Here again, the gametes being similar, 
the resulting body is a zygospore. The sexual process does not occur 
very often. 

It is to be remembered that molds are plants. But growing as they 
do in the dark, they have no chlorophyl and do not make their own food. 
They feed on food already prepared, not on ordinary plant or animal food 
as does man, for example, but on decaying matter or on food that has 
already been digested by the host, either before or after assimilation. 

The so-called water-mold is both parasitic and saprophytic as it can 
thrive either on dead or living fish. Molds are said to be a degenerate 
form of green plants which have acquired a habit of making some other 
organism do their work for them, rather than build their own food by 
photosynthesis as plants usually do. 


There are many difficulties in the way of working out a satisfactory 
classification of the pathogenic fungi because botanists and pathologists 
do not always use the same name or employ the same method. Botanists 
classify fungi or mycetes ( ) as follows : 

1. Phycomycetes : algae-like fungi. (Fig. 99.) 

2. Ascomycetes: sac-fungi (asci) ; asexual spores formed in sacs. 
(Fig. 100.) 

3. Basidiomycetes : spores, borne on little club-shaped hyphae, or 
basidia. (Fig. 101.) (Includes smuts, rusts, and mushrooms.) 

Pathologists take the following points into consideration and 
arrange their classification under the title of pathogenic protophytes : 

Most infectious diseases due to vegetable parasites are caused by 
bacteria, but a few owe their origin to micro-organisms of a higher type, 
namely, to the yeasts and molds. Two of the infectious processes caused 
by yeasts, although comparatively rare, deserve brief consideration. 
Both the organisms and the lesions they produce, microscopically and in 
gross, resemble each other more or less closely. For this reason they 
were for a long time confused with each other, but the differential char- 
acteristics are now fairly generally recognized. 

Simple Plants 211 

The relation of the yeasts or blastomycetes to the bacteria and the 
molds is shown in the following diagram : 

Pathogenic Protophytes. 

(These are all Chlorophyl-less plants.) 

~ ~r i : ~~ 

Schizomycetes ( ) | Hyphomycetes ( ) 

(bacteria) (molds) 

Blastomycetes ( ) 

Saccharomycetes ( ) 

Ascomycetes ( ) 


Oidia ( 
(transition form) 


A living organism may be injured either mechanically or chemically. 

Mechanical or physical injury may be the result of violence, pres- 
sure, heat (burning), cold (freezing), light rays, and electricity. 

Chemical injury results from poisons (toxins), whether by auto- 
intoxication, or toxins produced by animal or vegetable parasites. 

It is readily understood that a parasite may cause either mechanical 
or chemical injury to its host: the former by propagating so rapidly 
that it causes a physical obstruction, as is the case with the tubercular 
bacillus; and the latter by a definite poison that the foreign organism 
produces. The poison, or the mere mechanical effect, may in turn cause 
some out-of-the-ordinary conditions, as for example when it furnishes a 
stimulus to overgrowth on some part of the host, as galls on trees (a 
growth caused by the stimulus of aphids), or tumors in human beings. 
These latter are merely overgrown healthy cells. 

These overgrown healthy cells may press against neighboring blood 
vessels, obstructing the blood-flow and thus cause the death of the 
tissue which fails to receive its required amount of blood. 

It may be stated in this connection that there are some hosts which 
are not affected at all, or but little, by the poisons parasites produce, 
although the parasite itself does many such hosts a great deal of damage. 

The subject of toxins is among those of which no great knowledge 


General Biology 

has yet been obtained. Toxins are of great interest and importance as 
can readily be judged from what has been said. 

Probably, if toxins and enzymes are thought of here in relation to 
each other, it will lead to a clearer understanding of each. Both can be 
studied only by the effects they produce, the one injurious, the other 

One may also think of several other possibilities on the part of the 
invading organism. For example, it may live entirely at the expense 
of its host, in which case it is a parasite; it may live on decayed matter 
and do littre if any injury, and thus be a saprocyte; or it may actively 
engage in killing and devouring parasitic invaders and thus be of great 
value to its host. In the last instance it is known as a phagocyte. 

True yeasts grow by budding (Fig. 87) ; they rarely form mycelia; 
under unfavorable conditions of growth they may form endospores. 

Oidia grow by budding and as mycelia with spore formation. (Fig. 

Hyphomycetes (Fig. 98) grow as mycelia with spore formation of 
asexual or sexual origin. 

All authorities seem agreed that there is no sharp line of demarca- 
tion between the blastomycetes and the hyphomycetes, and most of them 
place the oidia as a transition form. 

Oidium, showing spores 
being cut off from the 
tip of the branch. Such* 
spores are called coindio- 

Fig. 103. 

Aspergillus Fumigatus. (After Brumpt.) 

Blastomycosis (also called saccharomycosis), is the term applied to 
the lesions produced by a blastomyces. A variety of organisms have 
been cultivated from the lesions, and different names have been assigned 
to them. It is not known if these are distinct entities. 

Simple Plants 213 

There is an infection in the skin, usually remaining localized there, 
but it may invade the circulation and cause lesions in other parts of the 

The blastomyces occur in human tissues only, as small round bodies 
with granular protoplasm, and with thick hyaline capsules. They mul- 
tiply by budding only in human tissues, but in cultures they may either 
develop mycelia or grow by budding or do both. They may be numerous 
in the lesions which they produce, or few and hard to find. 

They produce a fairly strong toxin. 

Aspergillus fumigatus (Fig. 103) is an example of the pathogenic 
ascomycetes. It is a fungus widely distributed, usually as a harmless 
parasite, having been found in the auditory canal, nose, and throat. 

In birds and in cattle, and more rarely in dogs, aspergillus may cause 
lesions of the lungs, resembling tuberculosis, and of late years a good 
many cases have been reported in man, particularly pigeon keepers and 
hair sorters. In the majority of these cases the infection is secondary 
to some long-standing affection of the lungs, though it also causes a 
primary lesion resembling broncho-pneumonia, usually quite serious. 
The patient coughs up a grayish-brown mass the size of a bean made 
up entirely of mycelium and spores. 

Oidiomycosis (granuloma coccidioides) is the term applied to the 
lesions produced by an oidium. In the past this organism has been 
called immities, coccidioides, etc., but it is not yet definitely classified 
by botanists. Infection with this organism is rare and is confined almost 
exclusively to California. The disease is practically fatal. 

The oidium occurs in human lesions in the form of spherical bodies 
which may reach a size of thirty microns. They consist of an irregularly 
staining mass of protoplasm enclosed within a double contoured capsule 
which is occasionally covered with prickles, or even long spines. The 
organisms multiply in tissues only by endosporulation, never budding. 
The spores may number as high as a hundred or more. They are 
liberated by the bursting of the capsule. The number of parasites in the 
lesions varies. The parasites may be many or few and hard to find. 
In cultures the oidium grows as long septate branching hyphae. In time, 
spores develop in the ends of the hyphae and are infectious. To inocu- 
lated animals, the hyphae, themselves, are not infectious. 

The lesions produced by oidium often bear a close resemblance to 
those caused by the tubercle bacillus, and have probably been mistaken 
for them more than once on histologic examination. If the organisms 
are few in number, a cheesy region may be formed, and if numerous, 
even abscesses and ulcers. 

Blood and lymph streams seem to carry the organism so that it is 
widely distributed. It is as likely to be found primarily within, as upon 
the skin of the body. 

Like the tubercle bacillus, oidium involves the same organs ; lungs, 
lymph-nodes, adrenal glands, meninges, seminal vesicles, etc. 


General Biology 

The skin lesions are chronic and consist of nodules, abscesses, and 


Actinomycosis or lumpy jaw. 


The Sporotrichoses. 

(a) Subcutaneous. Small solid nodules, becoming abscesses, ulcer- 
ating the skin. 

(b) Cutaneous. Principally in arms, hands and legs, though it 
may occur on other parts of the body. Ulcers form in groups of two or 

(c) Localized, hard and eroded on surface. 

Fig. 104. Sporotrichum Beurmanni. (After Brumpt.) 

1, Single lateral conidiospore; 2, terminal conidiospores; 3, 
collection of laterial conidiospores. 

The parasite (Fig. 104) is introduced by accidental inoculation, and 
possibly through the eating of grains and fruit. It acts like bacteria, 
producing toxins, toward which toxins there are active reactions of the 
body-fluids. It is a short rod 3 to 5 microns long and 2 to 3 microns 
in breadth. In cultures it grows in filaments of about 2 microns in 
diameter and forms characteristic ovoid spores. 

The points of differentiation between the various forms of this 
organism are due largely to the variation in its modes of sporulation. 

Simple Plants 


Fig. 105. Actinomyces Bovis. 
(After Rivas.) 

Parasite producing actinomycosis (lumpy- 
jaw). Actinomyces bovis, also called 
nocardia actinomyces, nocardia bovis, strep- 
tothrix actinomyces, streptothrix israeli, 
oospora bovis, cladothrix actinomycoses, 
and bacterium actinocladothrix. 

Nocardiosis. The parasites (Fig. 
105) resemble bacteria, on one hand, 
and on the other the hyphomycetes 
or molds, by forming branching, 
thread-like filaments, and by producing 
fine conidia. They represent a 
transition between bacteria and the 
lower fungi. The results of infection 
are similar to tuberculosis or multiple 
abscesses. Three cases have appeared 
as abscesses of the brain. 

Mycetoma or Madura disease. 

This disease is found principally in 
India, though it does occur in other 
parts of the world. There are great 
swellings of the foot, generally on the 
sole, nodular growths and multiple 
abscesses. Black, brownish, or yellow 
granules are formed, one micron in 

A variety of 
Streptothrix (Fig. 
106) has been found 
in the pale colored 
granules, closely re- 
sembling actinomy- 
ces. Most observers 
seem to hold that 
this Streptot hrix 
madurae and Acti- 
nomyces are distinct 
species. From the 
variety having black 
granules, a hypomy- 
cete has been grown, 
which is closely 
allied to Asper- 

non-bacterial fungi 


Fig. 106. Madurella Mycetoma. (After Brumpt.) 

In medicine, all diseases caused by any 
sometimes called Mycosis. 

It is worthy of note that medical men, being mostly interested in 
disease, take similar appearing lesions as their basis for classifying 
organisms, while biologists classify organisms according to structure 
and development, often with little reference to what disease such organ- 
isms may cause. 




BRYOPHYTES are usually said to possess archegonia ( ), 

or primitive egg gonads, composed of many cells, as contradistin- 
guished from the thallophytes which, when they possess gonads 
at all, are practically always composed of single cells. 

Bryophytes are moss plants and liverworts, and their life cycle con- 
sists of two stages, the sexual and the sexless. When these stages follow 
each other, an "alternation of generations" occurs. The sexual plant, 
or gametophyte, forms eggs and sperm which unite, while the asexual 
plant or sporophyte is the plant which grows from the fertilized egg of 
the sexual plant. This nonsexual plant forms asexual spores which, in 
turn, grow into gametophytes. 

Bryophytes may be quite simple, resembling the thallophytes, or 
they may form a leafy stem as in the mosses. 

There are some 12,000 different species of mosses or Musci, as they 
are technically known. These are divided into three distinct orders : 

1. Sphagnales ( ). The peat mosses. (Fig. 


Fig. 107. 
The Peat Moss, 


Fig. 108. Audreaea Petrophila. 
A, plant with mature sporophyte. 
B, longitudinal section of sporophyte. 
Ps, pseudopociium; col., columella. 
(From D. H. Campbell's "A University 
Text-Book of Botany," by permission of 
The Macmillan Co., Publishers.) 

Plant World Continued 


2. Andreaeales ( 


3. Bryales ( 

). The black mosses. (Fig. 
). The true mosses. (Fig. 109.) 


Fig. 109. A Common Moss. 

(Catharinea Undulata). 
Showing the branching leafy moss 
plants (gametophytes) attached to 
the rootlike mass of protonemal 
filaments and bearing sporophytes. 
(After Sachs.) 

Fig. 110. Sphagnum Acutifolium, Ehrb. 
A., prothallus (pr.) with_ a young _ leafy 
branch just developing from it; B., portion of 
a leafy plant; a., male cones; clu, female 
branches; C, male branch or cone, enlarged 
with a portion of the vegetative branch adher- 
ing to its base; D., the same, with a portion 
of the leaves removed so as to disclose the 
antheridia; E., antheridium discharging spores; 
F.j a single sperm; G., longitudinal section of 
a female branch, showing the archegonia 
(ar.); H., longitudinal section through a 
sporongonium, with dome of sporogeneous tis- 
sue; ar., old neck of the archegonium; /., 
Sphagnum squarrosum Pers.; d., operculum; 
c, remains of calyptra; qs., mature pseudo- 
podium; ch., perichaetium. (After Schimper.) 

The Sphagnales are the most primitive, and the Bryales the most 
highly developed. 

Sphagnum (Fig. 107) is a peat moss, growing, as its name implies, 
in swamps and along the margin of lakes. The peat bogs of northern 
regions are made up of thick clumps of this plant. Peat mosses are 
usually light green in color, bordering on white, and sometimes have a 
slight tinge of red and yellow. 

The plant has certain branches which bear reproductive cells, and 
other branches which are sterile. (Fig. 110.) 

The gamete plant (the one bearing the gametes or reproductive 
cells) has an upright stem with a mass of pith in the center. The outer- 
most portion is called the cortex. The cell walls in the cortex are thicker 
than those in the center, and often contain pigment. The cortex varies 
from two to four cells in thickness. The leaves are only one cell in 
thickness, and never have a midrib or other veins. In other words, 
there are no fibrovascular bundles in the stem. The lack of fibrovascular 
bundles is one of the great characteristics which distinguish this whole 
group of plants from the next higher grouping — the Ferns. 


General Biology 

As the leaves mature, a goodly portion of the cells increase in size, 
because the entire protoplasm is added to the walls of the cell so that 
these become very thick. This leaves the cell filled with nothing but 
air and water. In fact, this hygroscopic ( ) ability 

of the cells of Spagnum is the reason florists use the sponge-like 
Sphagnum in packing flowers for shipment. 

In those branches which are set aside for reproductive purposes, 
each sex uses individual branches for the antheridia (male branches) 
and the archegonia (female branches) (Fig. 111). In some species, 

Fig. 111. 
A Common Moss 

A, male plant, 
showing cup-like 
tip containing the 
antheridia. B., fe- 
male plant with 
the sporophyte; 
cal., cap, or calyp- 
tra, over the de- 
veloping spore 
case; C, a mature 
spore case with 
the calyptra re- 

Antheridia and Archegonia. 

Section Through 
the Tip of the 
Male Plant of a 

Moss (Funaria). 
a., antheridium; 

/., sterile filament, 

or paraphysis; /., 


Section Through 
the Tip of a 
Female Plant of 
a Moss (Funa- 
ria) . 

A., group o£ 
archegonia a. ; I., 
leaf. B, an arche- 
gonium in detail, 
showing enlarged 
basal portion e. 
with the egg, and 
the neck n. above 
with its row of 
canal cells ; m., 
mouth. (After 


(From Bergen & Davis' "Principles of Botany, 
sion of Ginn & Co., Publishers.) 

by permis- 

entire plants are of one sex or the other. In these, therefore, antheridia 
and archegonia are never found on the same plant. Such plants are said 
to be dioecious (from two households), while those plants, on which 
both male and female reproductive branches appear, are said to be 
monoecious (from one household). 

The branches bearing antheridia are called antheridophores. An 
antheridium is found in the axil ( ) of each leaf of the 

head and consists of a stalk composed of not more than four rows of cells. 
When the antherium is mature, it contains many sperm. 1 (Fig. 112.) 
The sperm are coiled, and bear two long thread-like cilia at their anterior 

1 Botanists use "sperms" for the plural of "sperm," while zoologists do. not. We have r there- 
for, kept the term "sperm" throughout as meaning both singular and plural. 

Plant World Continued 


end. There is a small appendage, called a vesicle, which contains starch 
granules. As the antheridia ripen, the sperm-sac is forced open, and this 
sperm discharged. It is important that this sperm-sac be not confused 
with the spore-capsule to be mentioned later. 

The branches bearing archegonia are called archegoniophores and 
are usually found toward the upper portion of the plant, while the 
archegonia themselves are at the tip 
of the archegoniophores (Fig. 113). 
Each archegonia has a neck, neck- 
canal, a venter which contains the egg, 
and a basal or pedicel. The archegonia 
of ferns will also be found to be quite 
like this, except that the pedicel is 
missing. Usually, several archegonia 
are found on a single branch. A num- 
ber of enlarged leaves surround the 
archegonia. They constitute a peri- 
chaetium ( ). 

Both archegonial and antheridial 
The ctmmon d M?ss° £ a Drancnes begin growing close together, 
(Funaria). but the main branch, from which both 

a., Anthendium; b., 1 1 . . 

escaping sperm; c, develop, continues growing between 

a single sperm in its .1 j ,- .1 >. ,1 1 bryo sporophyte (em.) 

parent cell. (After them and Separating them further and developing in the ven- 
Sachs.) further ter * ^fter Schimper.) 

Fertilization probably occurs in winter as young embryos are found 
in abundance in the spring. A film of water is needed for the purpose of 

Fig. 113. 
_ Sphagnum, 
showing a young em- 


Fig. 114. The Sporophyte of the Peat Moss 
A., group of the sporophytes on stalks, which are 
really growths from the gametophyte. B., longi- 
tudinal section through a sporophyte, showing the 
large foot imbedded in the top of the stalk; a., the 
remains of the parent archegonium, with the neck 
still present; s., a spore chamber; c, cover. (From 
Bergen & Davis' "Principles of Botany," by permis- 
sion of Ginn & Co., Publishers.) 


General Biology 

fertilization because sperm must swim to the neck-canal and pass through 
this into the venter. Here it enters the egg where the nuclei of sperm 
and egg unite. The fertilized egg now divides by mitosis very rapidly, 
and the upper cells form a large globular spore-case with a thick central 
column within known as the columella. This is surrounded by a dome of 
spores, around which the wall of the sporangium is formed. The spore- 
case later pushes against the wall of the archegonium by enlarging. 
The wall is then ruptured, the top portion remaining as the calyptra 
( ) (Fig. 119), while the spore-case later opens by 

means of a lid. The lower cells produced by the dividing oosperm 
become a swollen foot, which is imbedded in the tissues below. It re- 
mains connected with the spore-case by a short stalk. 

The structure, which thus develops from the fertilized egg-cell, is 
called the sporophyte (Fig. 114) stage of sphagnum. In fact, all such 
simple plants which develop spores are called sporophytes. 

Simultaneously with the maturing of the sporophyte, the apex of 
the female branch elongates into a leafless stalk about half an inch or 
more in length, known as the pseudopodium. It is supposed that the 
reason that the pseudopodium and sporophyte grow thus simultane- 

Antheridium of Pteris (B.), showing wall Fi 2- 116 - Sphagnum sp. 

cells (a.), opening for escape of sperm mother 

cells (e.), escaped mother cells (c), sperms A., B., young protonemata; C, older pro- 
free from mother cells (b.), showing spiral tonema with leafy bud, k.; r., marginal 
and multiciliate character. (After Caldwell.) rhizoids. (After Campbell.) 

ously, is probably due to the fact that cells in the foot secrete a substance 
which stimulates the cells to divide and enlarge, resulting finally in the 
formation of the pseudopodium. The advantage the plant gains is that 
the spore-case is raised to a higher plane, and it can thus throw its 
spores much farther than would otherwise be the case. 

As Sphagnum possesses no chlorophyl, it does not manufacture its 
own food and must, therefore, live on the absorption of food-matter from 
the gamete plant through the foot. 

The spores themselves develop in the following manner (Fig. 
115). In the spore-case the inner cells differentiate into two kinds, one 
making up the larger portion of the tissues, and the other, larger and 
richer in protoplasm, forming a dome of sporogenous or spore-forming 
tissue near the upper wall. It is from this latter type of cell that the 
spore-mother-cells are developed. 

Plant World Continued 


These spore-mother cells are divided twice, thus producing four 
spores each, and it is these spores which eventually germinate and pro- 
duce the gametophytes. In ferns, we shall see that a quite similar 
process of spore formation takes place. 

During the time the spores are maturing, a circular groove, called 
an annulus, forms near the apex of the spore-case. The cells in this 
region have thinner walls than the surrounding cells. These cells later 
become dry, and the thinnest part becomes torn 
to form a lid or operculum ( ) 

at the summit of the spore-case. As the opercu- 
lum falls away, the sperm are dispersed. 

If they find suitable soil, a short green pro- 
tonema (Fig. 116) germinates. The tip of the 
protonema broadens to form the prothallus 
which is one cell in thickness. Tiny rhizoids 

Sphagnum Cuspidatum, 
showing innovation, or 
short, branches. (After 


side and from the margin, 
c o n t a i n i ng chlorophyl 
then develop. Often a 
thallus forms at the tip of 
each of these threads. 
From this thallus a leafy 
branch grows upward, 
and the sphagnum plant 
described is again a full- 
fledged adult organism. 
The plant, from the time 
it germinates from the 

) form on the under 
while other threads 

Fig. 118. I. 
The Sporophyte of a Common Moss (Funaria). 
A., young sporophyte j. attached to the leafy moss 
plant and covered by the calyptra cal. B., sporophyte 
with mature spore case sc. and calyptra cal. at the 
tip. C, spore case with calyptra removed; o., the 
cover (operculum. D., a stoma from the surface of 
the spore case. E., section of young spore case, show- 
ing the cylindrical central region of spore-producing 
tissue sp. F., the spore-producing tissue in detail. 
(From Bergen & Davis "Principles of Botany," by 
permission of Ginn & Co., Publishers.) 

Fig. 118. II Developing Sporophytes 
of a Common Moss (Funaria). 
A., very young stage, showing the 
early cell divisions of the egg; B., 
older sporophyte just before the 
archegonium a. is torn away from 
the gametophyte and carried up- 
ward as the calyptra. The base of 
the sporophyte has now grown down 
into the tip of the leafy moss plant 
(gametophyte) and is firmly an- 
chored to it. (After Sachs.) 

222 General Biology 

spore until the thallus develops, is the gametophyte. This is to be dis- 
tinguished from the adult plant which, as we have seen, is called the 

There is an asexual multiplication of sphagnum also. This is 
brought about by a sterile branch which develops more powerfully than 
the surrounding ones. Then, each year, as the old stem dies off below, 
the young branch becomes a ■ new plant. Sometimes little plantlets, 
known as innovation branches (Fig. 117), strike root and become inde- 
pendent plants. These innovation branches spring from close to the tip 
of the sterile branches. 

The life-cycle of Sphagnum may be summarized as follows : 


Sphagnum-plant (gametophyte) 

Antheridial branch Archegonial branch 

I I 

Antheridia Archegonia 

I I 

Sperm (male gamete) Egg (female gamete) 

I I 

Oosperm (zygote) 

I I 


I I 

Mature Sporophyte 

I I 


I- I 


Spore Spore Spore Spore ' Reduction 





Sphagnum-plant (gametophyte) 

The so-called true mosses (Fig. 109) have life-histories quite like 
that of sphagnum, although there are differences. In true mosses the 
protonema produces leafy branches (the true moss-plants), but it does 

Plant World Continued 



G., a 

Moss (Tetraphis 

showing gemmae; 

gemma enlarged. 

C. Stuart Gager's 

"Fundamentals of Bot- 
any," by permission of 
P. Blakiston's Son & Co., 

not produce a thallus. The leafy branches arise directly from the fila- 
mentous protonema. True mosses are both monoe- 
cious and dioecious. There is no pseudopodium 
(Fig. 118), but the stalk of the sporophyte which 
is very short in sphagnum, here elongates to form 
a seta, often more than an inch in length. 

The true mosses have little breathing pores 
called stomata at the base of the capsule. Sphagnum 
has the stomata, but they do not function. Chloro- 
phyl-bearing cells surround these stomata, so that 
in the true-mosses there is some food actually man- 
ufactured by photosynthesis. 

The sporophyte of the true mosses seems to 
occupy an intermediate position between sphagnum 
and the next higher group of plants, the Ferns. 
There is an increase in sterile tissue as we approach 
the ferns, and a decrease in fertile tissue in the 

From experiments so far performed it seems 
that every cell of the moss-plant can, like the tissue-animal Hydra, which 
we shall soon study, develop a protonema — that is, each cell is a poten- 
tial spore. Each protonema produces buds which become mature plants. 

There are certain species of mosses in which the leafy-shoot, and 
in others, the protonemata, give rise to a special type of small bodies 
called gemmae (Fig. 119) ( ), which become sepa- 

rated from the parent plant and give rise to new plants. 

A comparison of Sphagnum and a fern (to be studied next) is of 
value here. 

The commonly known "fern-plant" is a sporophyte while the Sphag- 
num-plant is a gametophyte. 

The fern sporophyte is dependent on the gametophyte for nutrition, 
at first, then the sporophyte becomes entirely independent, while the 
simple gametophyte perishes. 

The Sphagnum sporophyte is the simpler plant and it is this sporo- 
phyte which must depend upon the gametophyte for nutrition through- 
out its entire life. 

Reproduction is quite alike in Fern and Sphagnum. Each produces 
haploid gametes of two sexes, which then unite in fertilization, the 
zygote being diploid. It is the zygote which produces the spore-bearing 
phase. The spores, which are in turn haploid due to a reduction having 
taken place, then give rise to the haploid gametophytes, so that we may 
sum up the life-cycle in both Fern and Sphagnum by saying: Gameto- 
phyte alternates with sporophyte, fertilization with reduction, gametes 
with spores, haploid cells with diploid. 

224: General Biology 

It will be seen from what has been said, that this whole group of 
plants shows a differentiation of cells into tissues, while in the higher 
forms leaf-like structures appear. Then the rhizoids (specialized absorb- 
ing organs) are developed, and the plant tissues themselves contain 
chlorophyl. It is supposed that bryophytes have evolved from aquatic 
forms to land forms, and consequently, as parts of the plant have dried, 
various structural adaptations ( ) have been brought 



These are the ferns (Fig. 120) and their allies in which the dis- 
tinguishing feature is that these plants possess nearly everything that 
thallophytes and bryophytes possess, plus a conducting or vascular 

These plants are supposed to have arisen "from a bryophyte ances- 
try where the sporophyte (sexless) generation, in some plants capable 
of doing chlorophyl work, developed a root system and vascular tissue, 
and taking the land habit, became independent of the gametophyte. 
This was one of the most important forward steps in the evolution of 
the higher plants, for it gave the sporophyte complete freedom to live 
and grow to its maximum size. This change marked a turning point 
in plant evolution, for, after the sporophyte became the most complex 
and conspicuous phase of the life-history, the gametophyte grew less 
prominent, until in the seed-plants the sexual generation became actually 
dependent or parasitic upon the asexual generation. This is a relation 
which is exactly the reverse of that which exists between the gameto- 
phyte and sporophyte in the liverwort and mosses." 

"After the sporophyte became independent of the gametophyte, the 
next important advance was the development of the lateral spore-bear- 
ing and vegetative organs called fronds ( ). Then 
came the differentiation of the frond into vegetative leaves, given up 
entirely to chlorophyl work, and spore-leaves (sporophyls) devoted 
chiefly or wholly to spore production. With this also, came the massing 
of the sporophyls into cones, which was really the beginning of the 
structures called flowers in seed plants." 

The pteridophytes have underground stems (root-stocks or 
rhizomes) so that only the leaves appear above ground. There is a 
terminal bud at the tip of the fern-stem. The rhizome bears true roots, 
and its tissues are differentiated into epidermal, fundamental, mechanical, 
and conducting systems. In the tropics there are tree ferns, many of 
which have been found among the fossil plants. 

The spore-cases grow in groups, called sori ( ), 

on the underside of the leaves (Fig. 121). As the annular ring about 

each individual spore-case dries up, that side which is thinnest and has 

become dried most, splits open, throwing out the spores. There are 

Plant World Continued 


usually 64 spores in each sporangium. These spores drop on to the moist 
earth and grow into a minute plant, by first absorbing moisture, and 
then, as the osmotic pressure becomes too great on the inner portion, 
breaks, and sends out a tiny tube (Fig. 122). This process is called 
germination ( ). Then a smaller tube appears 

close to the spore body growing from the tiny tube just mentioned, 
and this is the beginning of the root-like bodies, the rhizoids, which are 


Fig. 120. The Ferns and Their Allies. 

A. Fern plant (Aspidium), showing roots, rhizome, and frond: A., section 
of fruit dot (sorus), showing spore cases, some of which are ejecting their spores; 
B., portion of a leaflet, showing unripe fruit dots; C, portion of a leaflet, showing 
ripe fruit dots. (After Strasburger.) 

B. Order I. Salviniales (Floating Allies of ferns). Salvinia natans. 

C. Order II. Equisetales. Branched Equisetum. Equisetum Funstoni, com- 
monly called "Scouring Rushes," as distinguished from the "Horsetails" (also 
called Equisetales). The stems of Horsetails die each year and the fruiting cones 
have no terminal point. 

D. Field Horsetail, showing buds and tubers. 

E. Order III. Lycopodiales (Club-mosses). Common Club-moss, LycopoJiitm 

F. Order IV. Isoetales (Quillworts). Braun's Quillwort, Isoetes cchinospora 

(A, after Strasburger; B to F, from W. C. Clute's "The Fern Allies," by 
permission of The Frederick A. Stokes Co.) 


General Biology 

to hold the plant in place and absorb moisture and food material from 

the ground. 

This minute plant, which de- 
velops from the spore, is called the 
prothallium ( ). It 

is often heart-shaped. A portion 
just posterior to the notch, called 
the cushion, is several cells thick, 
and the outer part, called the wings, 
is only one cell in thickness. 

Near the notch of the heart, 
close to the cushion, several flask- 
shaped bodies, called arehegonia, are 
formed. Each archegonium contains 
an egg cell. Among the rhizoids 
are the sperm gonads, called anthe- 
ridia ( ). Many tiny 

motile cells are found in the anthe- 
ridia at maturity, but as these are 
discharged and find a small amount 
of moisture, they reach the egg and 
fertilize it. 
It will thus be seen that here, too, as in the mosses, there is an 

alternation of generations, the ordinary fern being the asexual plant 

and the prothallus the sexual. 

Fig. 121. 
A., a leaflet of the frond viewed from be- 
low to show the position of the sori. B., de- 
tails of the sori and veining on a portion of a 
leaflet. C, section of a sorus; i., indusium; 
s., sporangia. D., a spore case or sporangium, 
showing the opening from which the spores 
(sp.) have been discharged; r., ring. (From 
Bergen & Davis' "Principles of Botany," by 
permission of Ginn and Co., Publishers.) 


This group includes the plants which bear flowers like the rose and 
lily, as well as such flowerless groups as the pines which have their 
reproductive organs in cones or clusters, and are by no means so con- 
spicuous as are those contained in a real flower. 

Two older groupings of these higher plants are : 

Phanerogams ( ). The flowering plants. 

Cryptogams ( ). The non-flowering plants. 

This grouping is one that came into existence before the sexual 
processes of plants had been studied to any extent, and so is not accurate, 
because the so-called hidden processes of the cryptogams are in reality 
more evident than those of the complicated phanerogams. As the seed 
is the all-important part of a plant from the reproductive point of view, 
the name spermatophyte has become popular. Seed plants, like ferns, 
are sporophytes, though there is a gametophyte generation in their life- 
history, but it is so reduced in structure that it is quite difficult to see. 
The seed must, therefore, be studied. 

It can readily be understood that the seed, having a hard covering, 
which is wonderfully adapted for a protective purpose, lends itself well 
to long vitality, and makes it possible for the embryo to develop so far 

Plant World Continued 


Fig. 122. 
I. The Fern Prothallium and Archegonium. 

A., stages in the germination of the spore. B., young prothallium, showing 

first appearance of wedged-shapecl, apical cell x. C, tip of prothallium beginning 

to take on the heart-shaped form; x., apical cell. D., mature prothallium, showing 

group of archegonia on the cushion just back of the notch, and antheridia further 

back: rh., rhizoids. E., an open archegonium with egg ready for fertilization, 

and two sperms near the entrance of the neck. (A., B., C, E., after Campbell; 
£>., after Schenck.) 

II. The Antheridium and Sperms of a Fern (Onoclea). 

A., small prothallium with many antheridia an. : s., old spore wall. B., 
antheridium, showing cover cell c, ring cell r., and basal cell b., inclosing the sperm 
mother cells. C, antheridium opening. D., sperms. (After Campbell.) 

III. Diagram of a cytological life-cycle, based on a hypothetical fern with four 
chromosomes in the sporophyte. The nuclear phenomena are based on those of the 
thread-worm (Ascaris). Each chromosome is designated by a characteristic mark 
so that it may be traced throughout the diagram. (After R. F. Griggs.) 

within its protective covering that it can take root and establish itself 
readily when the time is ripe. Then, too, the seed is a storage organ 
of condensed food for the embryo. 

The pollen grain of seed plants produces a male gametophyte which 
bears either sperm or sperm nuclei. 

In the ovule of seed plants there is a megaspore which produces an 


General Biology 

Fig. 123. — Morphology of typical monoco- 
tyledonous plant. A, leaf, parallel-veined ; B, 
portion of stem, showing irregular distribu- 
tion of vascular bundles; C, ground plan of 
flower (the parts in 3's) ; D, top view of 
flower; E, seed, showing monocotyledonous 
embryo. (From C. Stuart Gager's "Funda- 
mentals of Botany" by permission of P. 
Blakiston's Son & Co., Publishers.) 

Fig. 124. — Morphology of a typical dico- 
tyledonous plant. A, leaf, pinnately-netted 
veined; B, portion of stem, showing concen- 
tric layers of wood; C, ground-plan of flower 
(the parts in 5's) ; D, perspective of flower; 
E, longitudinal section of seed, showing dico- 
tyledonous embryo. (From C. Stuart Gager's 
"Fundamentals of Botany" by permission of 
P. Blakiston's Son & Co., Publishers.) 

embryo sac in which the egg is formed. The pollen grain produces an 
outgrowth, or pollen tube, which penetrates the tissues surrounding the 
egg, and thus the sperm is carried to the egg, fertilizing it. 

Seed plants are commonly divided into 

Monocotyledons ( ). Example, lilies, corn, and 

grasses. (Fig. 123.) 

Dicotyledons ( ). Example, beans and cotton. 

(Fig. 124.) 

The drawings of various stem cross sections will illustrate the dif- 
ference in the structure of the two types of seed plants. (Fig. 125.) 

Angiosperms. — In this type of plant the ovules are produced in a 
closed ovary composed of one or more carpels ( ). 

The ovules become seeds, and the carpels and surrounding parts con- 
stitute a fruit. This fruit may consist of the ripened ovary only, or it 
may include the calyx ( ) and receptacle also. 

Plant World Continued 


Fig. 125. A. — Diagrammatic Cross-section of Stem of Indian Corn (endogenous or 
monocotyledonous plant). cv, fibro-vascular bundles; gc, pithy material between 
bundles. B, Diagrams of stem sections (exogens or dicotyledonous plant). a, 
cross-section of chickweed stem, the inner circle representing the cambium ring, 
the two radial lines indicating the portion enlarged in b; e, epidermis; h, hair; 
c, cambium-separating between p, phloem and w, woody portions of bundles; 
v, spiral vessels in the woody portion; x, pith and y, common parenchyma of 
bark; c, segment of a sunflower stem; p, parenchyma; b, bast fibres; s, sieve 
tube; c, cambium; g, vessels, pitted and spiral; h, wood fibres; d, one year, and 
e, four year old woody stems, illustrating the increase of vascular bundles. (From 
Needham's "General Biology" after Wettstein, by permission of The Comstock 
Publishing Co.) 

As no seed can be formed unless the reproductive organs, stamen 
( ) and pistils ( ) are present, 

these are called essential organs, and plants having both essential organs 
in a single flower are called perfect flowers, while those having only one 
or the other essential organs, are called imperfect. 

If a flower possess, in addition to the essential organs, a calyx 
( ) and a corolla ( ), it is called 

a complete flower. 

All of these parts are better understood from a study of Figure 146 
than from any description which could be given. 

Fig. 126. 
Three Growth Zones, showing 
arrangement of the Fundamen- 
tal Tissue Layers in roots and 
stems. 1, Dermatogen zone. 2, 
Periblem zone. 3, Plerom zone. 
(After C. W. Ballard's "Vege- 
table Histology," (Courtesy of 
John Wiley and Sons.) 


A correct understanding of plant tissues 
can, however, come only from a knowledge 
of how such tissues develop. 

Just as we shall soon see, hydra (because 
it is composed of tissues only) can regenerate 
almost any portion of the body, so, too, the 
early embryonic substance of plants is all 
quite alike, and can develop into many and 
varying types of cells. This early undiffer- 
entiated embryonic plant tissue is known as 
meristem. It is from this meristem that 


General Biology 

the so-called primary tissues develop. How- 
ever, in the early embryo, even while all the 
cells are quite alike, it is possible to suggest 
a division into three zones (Fig. 126), in each 
of which certain particular structures will ulti- 
mately grow. 

The diagram shows an outer, or dermato- 
gen region, a more interior, or periblem region, 
and an innermost, or plerom region. It is in 
the dermatogen zone that the first covering- 
tissues develop, while the periblem zone gives 
rise to the covering-tissues of the mature 
plant. All other structures arise in the plerom 

Fig. 127. 

A, longitudinal section through 
the root tip of spiderwort, showing 
the plerome (pi), surrounded by 
the periblem (p), outside of peri- 
blem the epidermis (e) which dis- 
appears in the older parts of the 
root, and the prominent root-cap 
(c). (After Land.) 

B, diagram of a root hair; CM, 
cell membrane; CS, cell sap; CW, 
cell wall; P, protoplasm; N, 
nucleus; S, soil particles. 

Fig. 128. Arrangement of the Pri- 
mary Tissues in the Root. 

1. Epidermis. 2. Hypodermis. 3. 
Primary Cortex. 4. Endodermis. 
5. Xylem bundle. 6. Pith. 7. 
Phloem bundle. (After C. W. Bal- 
lard's "Vegetable Histology." Cour- 
tesy of John Wiley and Sons.) 

The original cell-masses which constitute the three zones men- 
tioned above, are known as fundamental tissues up to the time the pri- 
mary tissues can be seen. 

In the dermatogen of the root, three distinct primary tissues de- 
velop. The outermost layer at the root-tip (Fig. 127) is the root-cap. 
This becomes thickened and protects the more delicate structures as the 
process of growth forces the root-cap through the soil. 

The epidermal cells above the root-cap give rise to root-hairs, which 
are important absorption organs. 

Above that portion of the root, which is covered with root-hairs, 
there are thick-walled epidermal cells. These form the primary 

In the periblem zone there are also three primary tissues. (Fig. 

Plant World Continued 


128.) The layer bordering on the primary epidermis is known as the 
hypodermis ( )• This layer is made up of thick- 

walled cells which are usually angled. The layer joining the plerome 

zone is the endodermis ( 

Fig. 129. 

). The cells in this layer 
are also thick-walled and resemble those. of 
the hypodermal layer. Between hypoder- 
mal and endodermal layers there are several 
layers of cells which constitute the primary 
cortex or cortical parenchyma ( ). 

The cortical parenchyma is made up 
largely of undifferentiated original periblem 

It is in the plerom zone (Fig. 129) 
where the most striking changes in the cell 
walls take place. Groups of cells have 
their walls thickened by the deposition of 
lignin ( ), which forms the 

fibrous elements that give strength to the 
plant. Such fibrous elements are known as 
prosenchyma ( ). The 

Diagram to illustrate secondary 
growth in a dicotyledonous stem 
which takes place in the plerome 

R, the first-formed bark; p, 
mass of sieve cells; ifp, mass of 
sieve cells between the original 

wedges of wood; fc, cambium of conducting elements are developed in the 

wedges of wood; ic, cambium be- m . . n 

tween wedges; b, groups of bast midst of these llgnified Cells. 

cells; fh, wood of the original 

wedges; ifh, wood formed between 

wedges; x, earliest wood formed; 

(c). (After Land.) 

Each group of lignified cells, together 
with its associated ducts, constitutes the 
xylem ( ). This 

is usually arranged in a very definite order in the plerom region. There 
are other cells forming tubes, also in the plerom zone. The end walls 
of these cells are perforated. These form the sieve tubes. Each group 
of sieve tubes with its associated companion cells, parenchyma cells, 
and lignified tissues, constitutes the phloem ( ). 

These bundles are also often arranged in a very definite order. 

The lignified cells of xylem are called wood fibers (Fig. 130), and 
the lignified cells of phloem are called bast fibers. 

Xylem and phloem are made up of both fibrous and vascular (con- 
ducting) elements to form fibro-vascular bundles. 

The xylem and phloem are located in a circle near the outer boundary 
of the plerom region, and as they begin to develop, usually alternate- 
with one another. 

As there are narrow strips of unchanged plerom parenchyma ex- 
tending between the fibro-vascular bundles (Fig. 131), these strips 
present the appearance of rays, and consequently are known as 


General Biology 

Fig. 130. Types of Wood and Bast Fibers. 

medullary rays, while the 
unchanged parenchyma in 
the center of the plerom is 
the pith. 

In many orders of 
plants it is these primary 
tissues which remain 
throughout life with but lit- 
tle change, but in the higher 
orders these primary tissues 
change to secondary, or 
permanent, tissues. (Fig. 

The epidermis is re- 
placed by a bark structure 


A, cross section of bast fibers from stem of Aristolochia i • 

Siphu showing stratification.^ B, Portion of bast fiber, WfllCll Originates 111 

showing oblique striation. C, Portion of bast fiber show- r><=»riK1p»m -ren-r-ir^n 

ing transverse striation. D, Bast fiber from the bark of pcllUiem region. 

Some of the primary 

Cinchona Calisaya, showing longitudinal striae and small 
tubes connecting the lumen of the cell with the exterior. 
(From Bastin's "College Botany." Courtesy of G. P. 
Engelhard & Co.) 

cortical cells become meristematic, 
thus constituting the cork cambium 
or phellogen ( ) ; 

these cells subdivide rapidly to form 
a new tissue on their outer surface, 
the cork, and on the inner surface, 

Bark is everything outside of 
the true cambium (not the cork 
cambium), excluding the cambium 
and epidermis. 

The phellogen retains its meris- 
tematic power throughout the entire 
life of the plant so that new pro- 
tective tissues can keep pace with 
the internal growth. 

The primary fibro-vascular 
bundles consist of xylem and phloem, but in the change to secondary 
structures, a meristematic tissue, called cambium ( ), 

develops in connection with these. The cambium develops on the 
outer face of the xylem (Fig. 133) and on the inner face of the phloem, 
so that the cambium arc on each xylem bundle produces xylem on 
its inner face and phloem on its outer side. 1 Similarly, the cambium 
arc on the phloem bundle develops xylem on the inner side and phloem 
upon the outer. 

Fig. 131. Medullary Rays and Pith. 

A, Pinus Virginiana, cross section of 
two-year-old branch. P, pith; x, wood, show- 
ing two annual rings; cam, cambium; ph, 
phloem; r, resin-ducts in the cortex. B, Pinus 
insignis, cross-section of the inner part of the 
wood. P, pith; t 1 , primary tracheae; t-, 
secondary tracheids; r, resin-ducts; m, medul- 
lary ray. (From D. H. Campbell's "A Uni- 
versity Text-book of Botany," by permission 
of The MacMillan Co., Publishers.) 

^ylem and phloem both carry water, but the former carries food material as such, while the 
latter carries food in the water. 

Plant World Continued 


Fig. 132. 

Arrangement of Secondary Tissues 
in Roots and Stems. 

1. Peridem (bark). 2. Phellogen. 3. 
Phelloderm (bark). 4. Phloem elements. 5. 
Cambium. 6. Xylem elements. 7. Medullary 
rays. Compare with Fig. 129. (After C. W. 
Ballard's "Vegetable Histology." Courtesy of 
John Wiley and Sons.) 

This causes each fibro-vascular 
•bundle now to consist of xylem and 
phloem elements, separated from 
each other by a thin strip of cam- 
bium. Such bundles, which have 
been completed by the cambium, are 
called complete fibro-vascular bun- 
dles, while those not so completed 
are known as incomplete fibro-vas- 
cular bundles. (Fig. 134.) 

As the cambium continues 
to grow constantly, the plerom 
parenchyma becomes almost en- 
tirley replaced by xylem. The new 
hbro-vascular bundles develop in the broad primary medullary rays. 

The stem and root development differ somewhat. There are no 
root hairs or root-caps on the stem. The primary stem epidermis often 
possesses stomata (breathing pores), 
while the root does not. The 
parenchymal cells of the stem often 
contain chloroplasts which the 
parenchymal cells of the root never 
do. Then, too, the root has no hypo- 
dermis (mechanical tissue imme- 
diately underneath the epidermis). 
There is usually no endodermis in the stem, though there is in the root. 
The plerom zone of primary stems differs considerably from that of 

primary roots both in the arrange- 
ments and development of tissues. 
All fibro-vascular bundles in the 
plerom region of the primary stem 
are complete, showing phloem, 
xylem, and cambium elements 
throughout their entire period of 
growth. This means that the pri- 
mary fibro-vascular bundles of the 
stem are really equivalent to the 
secondary bundles of the root. The primary stem structures, described 
above, serve throughout the life of the plant only if such plant is an 
annual. In perennials ( ), a better and 

more durable covering tissue must be developed. In these, the primary 
epidermis is replaced by periderm tissues which have been produced by 
a phellogen which in turn developed in the primary cortex. The peri- 


Fig. 133. Diagram Showing the Method by 

which the Cambium Layer Produces Wood 

Cells on its Inside and Bark Cells on 

the Outside. 
be, the cells of the bark; c, cambium cells; 
xvc, the wood cells. 

Fig. 134. Completion of Fibrovascular Bundles. 
F, Completed fibrovascular bundle. 1. 
Xylem elements. 2. Cambium. 3. Phloem ele- 
ments. (From C. W. Ballard's "Vegetable 
Histology," Courtesy of John Wiley & Sons.) 


General Biology 




derm of stems is often ruptured and cast off as the inner tissue expands. 
This does not occur in roots. When such casting off takes place, the 
primary periderm is replaced by secondary periderm which develops 
directly from the original phellogen or secondary phellogen layers. The 
hypodermal and endodermal layers disappear as soon as the phellogen 
is formed in the primary cortex. The primary fibro-vascular bundles 

become larger by new 
a xylem and phloem ele- 

ments added by the cam- 
bium, and the cambium 
arcs extend until they 
become a complete ring 
or circle. 

New fibro-vascular 
bundles form in the broad 
medullary rays extending 
between the original bun- 
dles, while new woody 
elements are being added 
to the xylem. These 
woody elements, however, 
never entirely replace the 
original plerom tissue in 
the center of the stem. 
This unchanged central 
plerom tissue is the pith. 
As the plerom paren- 
chyma is entirely replaced 
by woody tissues in roots, 
the presence of pith is val- 
uable in distinguishing 
stem from root. 

The secondary or per- 
manent stem tissues are 
often divided into parenchyma ( ) and prosenchyma. 

Parenchymal cells may be found in all three zones of the embryo. They 
have thin walls and protoplasmic contents. Prosenchymal cells are 
formed in the plerom region of the embryo. They have thick walls, and 
the protoplasmic contents are very inconspicuous or even entirely lack- 
ing. While these distinctions are by no means absolute, they are of 
great importance. Further, prosenchymal cells are usually spindle- 
shaped, while parenchymal cells are more inclined to be spherical or 
cubical with rounded corners. (Fig. 135.) 

Fig. 135. 

A. Early undifferentiated cells known as Embryonic or 
Meristem tissue 

B. The secondary (permanent) tissues are divided into 
parenchyma and prosenchyma. The former have thin wails 
and protoplasmic contents. They are found in the undiffer- 
entiated cellular structures of all three zones in the embryo. 
They are usually spherical in shape, or at least "as broad 
as they are long." Prosenchyma cells are formed in the 
Plerom region of the embryo. They have thick walls and 
little or no cell content. The cells are usually long fiber 
cells with sharp-pointed ends. 

a. Transverse Section, Triticum Rhizome. 1. Epidermis. 
2. Hypodermis. 3. Cortical parenchyma. 4. Endodermis. 
5. Fibers, surrounding sieve and ducts. 6. Sieve. 7. Ducts. 
8. Concentric fibrovascular bundle. 9. Pith parenchyma. 

b. Powdered Triticum Rhizome. 1. Epidermis. 2. Hypo- 
dermis. 3. Parenchyma, longitudinal view. 4. Endodermis. 
5. Fibers. 6. Vessels. (From C. W. Ballard's "Vegetable 
Histology," Courtesy of John Wiley & Sons.) 

Plant World Continued 


The final tissues are usually grouped according to their functions. 
They are : 

Covering or Protective Tissues. (Fig. 136.) Epidermis and 

Supporting or Mechanical Tissues. (Fig. 137.) All fibrous tissues, 
such as wood and bast fibers, stone cells (sclerenchyma), polygonal cells 
with very thick cellulose walls, especially thick at the angles (collen- 
chyma) which take the place of woody tissue in annual herbaceous or 
green stems, fruits, seeds, and leaves. Collenchyma is usually associated 
with the fibrous tissues in the midrib of leaves. 

5D900000 1 

Fig. 136. Epidermal Tissues. 

A, Sectional views of Leaf Epidermis. 1. Upper epidermis, Ficus leaf. 2. Lower 
epidermis, Ficus leaf. 3. Upper epidermis, Eucalyptus leaf. 4. Epidermis of Pine 
leaf. 5. Upper epidermis, Orange leaf. 6. Upper epidermis, Geranium (Pelargo- 
nium), leaf. E, epidermis. H, hair. 

B, Surface views of Leaf Epidermis. 1. Hepatica leaf (wavy walls). 2. Chima- 
philla leaf (beaded walls). 3. Henbane leaf (wavy and striated walls). 4. Senna 
leaf (angled cells). 5. Convallaria leaf (beaded walls). (From C. W. Ballard's 
"Vegetable Histology," courtesy of John Wiley & Sons.) 

Absorption Tissues. (Fig. 138.) Root-hairs for liquids, and 
stomata (openings usually on the underside of leaves surrounded by two 
sausage-shaped guard-cells) and lenticels (openings in the periderm or 
corky coverings of mature woody plants.) 

Conducting Tissues. (Fig. 139.) This consists of ducts known as 
tracheae if they are continuous tubes formed by the absorption of the 
connecting cell's end-walls, and there is a disappearance of the cell con- 
tents. These tubes may be pitted (when there are numerous pores 
through the cell wall), reticulate (when the lignin laid down on the 
inner side of the cell wall is in the shape of a network), scalariform 
(when the non-lignified portions of the cell walls form long narrow slits 


General Biology 

which are quite uniform). Such cells are often angled (no others are). 
Annular (thin-walled tubes with rings of lignified tissue within the 
lumen of the tube), and spiral (where the lignified tissue is arranged in 
the form of a continuous spiral-band, or collection of bands). 

Tracheids are merely single cells which have lost their protoplasmic 
contents, but not their entire end-walls. Communication is carried on 
by pores in the vessel walls. 

Sieve Tubes, unlike all the other ducts mentioned above, usually 
carry materials away from the leaves. They are merely individual cells 
whose end-walls have not completely 
broken down, as in the tracheids, but 
have formed sieve plates with many 
pores or perforations connecting one 
such individual cell with the next 
below, and so continuing for great 
lengths in the plant. The walls of 

Fig. 137. Mechanical and Supporting Tissues. 

These tissues consist of wood and bast fibers (See Fig. 130, sclerenchyma 
(stone-cells), and collenchyma. 

A, Portion of epidermis and collenchyma from the stem of Rumex crispus. 
Cross section, ep, epidermis; c, collenchyma. 

B, Sclerotic cells from the root of Apocynum androsaemifolium. All highly 
magnified. (From Bastin's "College Botany," courtesy of G. P. Engelhard & Co.) 

C, 1. Peppermint stem. Arrangement of collenchymatic (C), tissues at angles 
of the stem. 2. Peppermint stem. 3. Sabal seed. 4. Colchicum seed. (Porous 
type.) 5. Nux Vomica seed. (Striated type.) 6. Arrangement of collenchymatic 
tissues around the midvein of a leaf. C, collenchyma. (From C. W. Ballard's 
"Vegetable Histology," Courtesy of John Wiley & Sons.) 

sieve tubes are composed of cellulose, without a trace of lignification. 

Medullary Rays furnish the means by which material is transported 
laterally from the inner-tube region of the plant to the tissues which 
lie closer to the outside of the stem, and from these to the pith where 
food may be stored. 

Latex Tubes. These are non-porous tubes in certain plants and 
contain a milk-like fluid. 

Porous Parenchyma. In the pith region, the parenchyma, which is 
very porous, may possibly assist in permitting the nutrients in solution 
to pass back and forth. 

Plant World Continued 



As already stated, each group of vessels with its connecting mechan- 
ical or supporting tissue, forms a fibro-vascular bundle. These may be 

either complete or incomplete ; com- 
plete, if they possess xylem, phloem, 
and cambium elements ; and incom- 
plete, if they possess either xylem 
or phloem without the cambium ele- 
ment. The xylem is always sup- 
ported by wood fibers and the 
phloem by bast fibers. There are 
five different arrangements of fibro- 
vascular bundles : 

(1) Radial (common in all 
young roots, and sometimes in 
mature monocotyledonous roots). 
These are always incomplete, con- 
sisting of either xylem or phloem. 
The xylem or phloem elements are 
arranged in a circle within the endo- 
dermis, a xylem bundle alternating 
with a phloem bundle. 

(2) Concentric fibro-vascular 
bundles (common in monocotyledo- 
nous roots and stems), are bundles 
consisting of both xylem and 
phloem, so arranged that either 
the xylem surrounds the phloem or 

The former arrangement is the more 
common. The bundles are irregularly scattered in the pith region. 

(3, 4, and 5) Collateral fibro-vascular bundles are complete, having 
both xylem and phloem elements, as well as a cambium-arc. These are 
in turn divided into three types, known as open, closed, and bi-collateral. 

(3) Closed Collateral bundles (usually found only in the pith of 
monocotyledonous stems and rhizomes and in the leaves of all seed 
plants), are made up of a xylem portion and a phloem portion, never 
separated from each other by a strip of cambium. 

(4) Open Collateral bundles (most frequently found in dicotyledo- 
nous roots and stems) are made up of xylem elements with a cambium 
zone and phloem elements on the outer side of the cambium. 

(5) Bi-Collateral bundles (found in some dicotyledonous roots and 
stems) are made up of a xylem element and the associated cambium, but 
with two phloem elements, one on each surface of the xylem. 

Assimilating and Synthesis Tissues (Fig. 140). The Chloroplasts 

Fig. 138. Absorption Tissues. 

1. Root hairs (H) on rootlet of germinat- 
ing Fenugrek seed. C, root cap. 2. Stomata, 
surface view. A, breathing pore. G, guard 
ceils. B, bordering, neighboring or surround- 
ing cells. 3. Stomata, sectional view. A, 
breathing pore. G, guard cells. B, bordering 
cells. 4. Lenticel (A). (From C. W. Bal- 
lard's "Vegetable Histology," Courtesy of 
John Wiley & Sons.) 

the phloem surrounds the xylem. 


General Biology 

Fig. 139. Conducting Tissues. 

A. Collateral type, Bamboo stem. 1. Fibrous tissue. 2. Ducts. 3. Sieve. 

B. Collateral Bundle arrangement of fibrovascular elements. 1. Xylem. 2. 
Endodermis. 3. Phloem. 

C. Bicollateral Bundle arrangement of fibrovascular elements. 1. Phloem. 
2. Cambium. 3. Xylem. 4. Cambium. 5. Phloem. 

D. Open collateral type, Aconite tuber. 1. Bast fibers. 2. Sieve cells. 3. Cam- 
bium. 4. Wood fibers. 5. Ducts. 6. Medullary ray. 

E. Open Collateral Bundle arrangement of fibrovascular elements. 1. Phloem. 
2. Cambium. 3. Xylem. 4. Medullary ray. 

F. Radial type, Sarsaparilla root. 1. Endodermis. 2. Sieve surrounded by 
bast fibers. 3. Wood fibers surrounding sieve and ducts. 4. Ducts. 

G. Radial Bundle arrangement of fibrovascular elements. 1. Endodermis. 
2. Xylem. 3. Phloem. 4. Pith. 

H. Concentric type, Fern rhizome. 1. Endodermal sheath. 2. Sieve sur- 
rounded by small parenchyma. 3. Fibrous tissues. 4. Ducts. 

/. Concentric Bundle arrangement of fibrovascular elements. 1. Endodermal 
sheath. 2. Phloem. 3. Xylem. (From C. W. Ballard's "Vegetable Histology," 
Courtesy of John Wiley & Sons.) 

(the tiny divisions in the cell of 
important structures in synthesis 


Fig. 140. Assimilating and Synthesis Tissues. 

A. Plastids (chloroplasts) in a cell. 

B. Diagram to illustrate the processes of 
breathing, food-making, and transpiration 
which may take place in the cells of a green 
leaf in the sunlight. (After Stevens.) 

plants which contain chlorophyl), are 
by converting (when in the sunlight) 
carbon dioxide and other sub- 
stances into starches and sugars; 
and the Leukoplasts (similar struc- 
tures which do not contain 
chlorophyl), by assisting in form- 
ing storage or reserve-starch from 
the sugar manufactured by the 

Secreting cells and hairs which 
are really structures quite like the 
glands of animals. 

Storage Tissues (Fig. 141). In plants which continue their life 
throughout many seasons, there must be a method of storing the food 

Plant World Continued 


which is made primarily in the summer. The organs are the Paren- 
chyma cells of the cortical and pith regions. Here the reserve starch 
made by the leukoplasts is stored, as also are many other plant nutrients. 

Secretion cavities of various kinds carry oils and other products of 
giand cells. 

Collenchyma cell walls, especially in seeds and fruits, contain much 
cellulose. This means that collenchymal cells are both supporting and 
storage tissue as well as synthesis tissue. 

Fig. 141. Storage Tissues. 

These are the parenchyma cells of the 
cortical and pith regions of the plant; the 
cellulose in the collenchyma cells (which 
makes collenchyma a synthesis, supporting, 
and storage tissue), and cavities of stone 
cells and fibers. 

A, grain of corn, cut lengthwise; C, coty 
ledon; E, endosperm; H, hypocotyl; P, 

B, starch grains in the cells of a potato 

Fig. 142. Reproductive Tissues. 

Diagrammatic sections of sporogonia of 
liverworts: A, Riccia, the whole capsule being 
archesporium except the sterile wall layer; 
B, Marchantia, one half the capsule being 
sterile, the archesporium restricted to the other 
half; D, Anthoceros, archesporium still more 
restricted, being dome-shaped and capping a 
central sterile tissue, the columella (col). 
(After Goebel.) 

Cavities of stone cells and fibers may contain nutrient material in 
a few cases, but in such instances it is not readily available for the plant. 

Reproductive tissue (Fig. 142). From inner tissues of anther and 
ovary in flowering plants. 

When pollen is transferred from anther ( ) to 

stigma ( ) the process is called pollination. Wind, 

insects, and water are means by which pollen is carried from one plant 
to another. Bees are common carriers, and the remarkable way some 
plants are adapted to forcing any intruder to carry pollen with it, is one 
of the most astounding of all adaptations in nature (Fig. 239). 


Pollination can probably best be understood by considering the 
modern pines. In the common Scotch pine (Fig. 143), (Pinus silvestris) 
the microsporophyls (called stamens in the flowering plants) are 
massed into cones about one centimeter in length, and these cones are in 
turn massed in clusters. 

There are two sporangia on the lower surface of each microsporo- 
phyl. These microspores, or pollen, escape from the sporangia and are 
carried by the wind (often for many miles) to the megaspore (carpellate) 

The megaspore cones grow singly or in clusters near the ends of the 
upper twigs of the season's growth, and are also about one centimeter 


General Biology 

in length. There is a general axis on which flat megasporophyls are 
borne. Each of these megasporophyls bears two inverted megasporangia 
or ovules (Fig. 144). 

The pollen falls between the megasporophyls (called carpels in the 
flowering plants), and each microspore then pushes out a pollen tube 
which penetrates the ovule tissue. This process stimulates the growth 
of the cone tissues, and the cone, therefore, increases in size. The ovules 
also enlarge, and the upper end of the ovule develops a thickened mass 
of green tissue which grows beyond the end of the sporophyl, to form 
the seed scale. These seed scales are merely the distal ends of the ovules, 
and function as organs of photosynthesis for a year or so. 

Fig. 143. Scotch Pine (Pinus sylvestris). 

A-D, stages in the development of the carpellate cone, and its car- 
potropic movements. E, very young carpellate cone much enlarged; F, 
vetral, G, dorsal views of a scale from E; 1, ovuliferous scale; 2, ovule 
(in logitudinal section); 3, pollen chamber and micropyle leading to 
the apex of the nucellus (megasporangium) ; 4, integument of the ovule; 
G, 1, tip of ovuliferous scale; 5, bract; 4, integument; H, longitudinal 
section at right angles to the surface of the ovuliferous scale (diagram- 
matic) ; 6, megaspore; 7, pollen chamber, /, longitudinal section of a 
mature cone; 6, ovule; J, scale from a mature cone; 6, seed; w, wing of 
seed; K, dissection of mature seed; h, hard seed coat; c, dry mem- 
branous remains of the nucellus, here folded back to show the endosperm 
and embryo; e, embryo; p, remains of nucellus; L, embryo; c, coty- 
ledons; e, hypocotyl; r, root-end. (From _ C. Stuart Gager's "Funda- 
mentals of Botany," by permission of P. Blakiston's Son & Co., Publishers.) 

The following summer or autumn a spore-mother-cell, also known 
as an archespore, arises in the interior tissues of the ovule. This arche- 
spore then divides into four cells which are really four young mega- 
spores, although only the one lying in the lowest position actually de- 
velops into a full-fledged megaspore. 

This megaspore then divides and subdivides until a rather solid 

Plant World Continued 


cellular mass is formed. This cellular mass is the gametophyte. (Fig. 

It is from this gametophyte that several (usually four) sunken 
archegones arise. The completing process of fertilization may now take 

After fertilization the gametophyte becomes stored with food and 
functions as the endosperm. 

The pollen-tube has also resumed its growth by this time and has 

Fig. 144. I. Carpellate cone, carpels, and seed of the Scotch pine 
(Pinus sylvestris). 

A, young growth with carpellate cones, about three weeks 
after the opening of the terminal bud: n, young pine needles. B, 
inner and side view of a cone scale at the time of pollination as 
shown in A : b, bract; o, ovules. C, inner and side view of scales 
from a mature cone as shown in D : b, bract; o, fertilized ovules 
now rapidly maturing into winged seeds; w, the developing wings. 
D, a mature cone. E, a mature winged seed. F, section of 
™ n mature seed; t, hard seed coat, or testa, developed from the integu- 
ment of the ovule, n, a membranous seed coat which is the re- 
mains of the nucellus; en, endosperm or tissue of the female 
gametophyte; em, embryo with group of cotyledons c and the 
suspensor s; m, micropylar end of seed. 

<H„g. II. The staminate cone, stamen, and pollen of the Scotch pine 
(Pinus sylvestris). 

A, young growth, with staminate cones about two weeks 
after the opening of the terminal bud. B, details of cone. C, end 
view of stamen. D, side view of stamen. E, pollen mother cell 
developing four pollen grains in a tetrad. F, pollen grain show- 
ing the two wings; p, prothallial cell; g, generative cell; t, tube 
nucleus. — E, (After Miss Ferguson). 

III. White pine. 

(Pinus Strobus.) Longitudinal section through an archegonium at the time of fertilization. 
Above the fusing nuclei are various other elements emptied into the egg from the pollen-tube. Col- 
lected June 21, 1898. X about 62. s.g., starch grains; p.r., prothallium; c.p.t, cytoplasm from pollen- 
tube; st.c, stalk-cell; t.n, tube-nucleus; s.n, sperm-nucleus; e.n, egg-nucleus; n.s, nutritive spheres. 
(After Margaret C. Ferguson.) I, II, (From Bergen & Davis "Principles of Botany," by permission 
of Ginn & Co., Publishers). Ill, (From C. Stuart Gager's "Fundamentals of Botany," by permission 
of P. Blakiston's Son & Co., Publishers). 


General Biology 

brought the two non-ciliated sperm to the mouth of an archegone. One 
of the sperm fuses with the egg which completes fertilization. This 
fertilization takes place in the pines more than a year after pollination. 

*? &t-$^r®^T- 0*t 

Fig. 145. I. The Gametophytes of the Pine. 
A, diagram of a section of a year-old ovule; embryo sac with mature arche- 
gonia ar imbedded in the tissue of the endosperm (female gametophyte) ; pollen 
tubes (male gametophytes) growing down through the tissue of the nucellus »; 
p c, pollen chamber; m, micropyle; i, integument. B, germinating pollen grains, 
showing young male gametophyte; t, tube nucleus; g, generative nucleus; p, pro- 
thallial cell. C, tip of pollen tube applied to the egg; t, tube nucleus; s, the two 
sperm nuclei. D, a mature archegonium sunken in the tissue of the endosperm, 
showing the large egg surrounded by a jacket of cells rich in protoplasm: two neck 
cells of the archegonium shown just above the egg. — B, C, (After Miss Ferguson). 

II. The Sperm and Ovule of a Cycad (Zamia). 
A, lower surface of a stamen, with numerous pollen sacs in two groups. B, 
the two large top-shaped motile sperms at the end of the pollen tube ready to be 
discharged above the archegonia. C, a sperm viewed from the end, showing the 
spiral band which bears the cilia. D, diagram of a section of an ovule after polli- 
nation; m, micropyle; i, integument; £, pollen chamber; n, nucellus containing 
developing pollen tubes; a, archegonia, with large eggs imbedded in the endosperm 
(female gametophyte).— B, C, (After Webber). 

III. — Diagram of the life-cycle of a pine. (After Schaffner.) 
I., II., (From Bergen & Davis "Principles of Botany," by permission of 
Ginn & Co., Publishers). 

Plant World Continued 


The fertilized egg, now called a zygote, gives rise to the embryo 
which consists of a cylindrical ste*m with narrow whorled leaves and a 
root. It is still imbedded in the gametophyte tissue from which it draws 
its nourishment. 

The ovule, seed-scale, and cone have increased in size in the mean- 
time, and the seed-scales lose their chlorophyl and become woody. As 
the supply of water becomes less and less the cone becomes dry, and 
consequently the young sporophyte stops growing. The cone and seeds 
are now said to be ripe, so that as the dry seed scales are spread out and 
blown away, the part of the seed which contains the embryo, is carried 
with them. As soon as water is again supplied, the embryo again 
begins to grow, breaking the brittle integument or indusium covering it, 
and the root is ready to penetrate the soil and carry water to the stem 
and leaves of the new plant. 


The flowers of flowering plants (Fig. 146) consist of cone-like 
clusters of closed megasporophyls (carpels) above, and microsporophyls 

(stamens) below, subtended 
by a perianth. The plant on 
which the flowers grow is the 

The microspores or pollen- 
cells (Fig. 147), each produce 
a mature gametophyte which 
consists of a pollen tube with 
three nuclei (Fig. 148 B) ; 
one, the nucleus of the pollen 
tube itself, and the other two, 
sperm nuclei. 

The megaspore is retained 
within the ovule (Fig. 148 A), 
(megasporangium). A gameto- 
phyte with a single egg devel- 
ops within the ovule. After 
fertilization, the zygote devel- 
ops into an embryo and an en- 

Fig. 146. Floral Organs. 

A, Orange blossom.. (After Bailey.) 

B, llydrophyllum, cal, lobe of calyx; cor, lobe of 
corolla; st, stamens; p, pistil. (After Lindley.) 

C, Diagrams of flower, showing face-view and 
dissection. r, receptacle; se, sepal; pe, petal; st, 
stamen; pi, pistil; o, ovule. 

The parts of a complete bisexual flower of the 
higher seed plants (angiosperms) are sepals, petals, doSDerm, to be described 
stamens, and pistils. The sepals, taken together, 

constitute the calyx; the petals, taken together, con- shortly, while the entire OVllle 
stitute the corolla. The calyx and corolla are col- 
lectively known as the floral envelopes, or perianth. 

Many angiospernwus flowers consist of five cir- 
cles, or whorls, two of which belong to the perianth, 
two to the stamens, and one to the pistils. The parts 
of each circle alternate in position with those of the 
preceding or following one, and all the members of 
each circle are alike. (From Bergen & Davis "Prin- 
ciples of Botany," by permission of Ginn & Co., Pub- 

becomes covered with one or 
two coats to form the seed. 
With proper moisture and soil, 
the sporophyte escapes from 
the seed as with the pine. 
(Fig. 149.) 


General Biology 

The purpose of a flower is the production of seed. The ripened 
carpel, with its contained seed, is known as a fruit. (Fig. 150.) 

The buttercup (Fig. 151) will serve as an excellent example of the 
flowering plants. Here we have many carpels (simple pistils) each 
made up of an ovary (the simple closed cavity below) which gradually 
tapers to a soft terminal stigma. The carpels are flat and open when 
the plant is young, but they gradually have their margins curve upward 
and close. During the time the carpel is closing, an ovule grows out 
from the base and becomes enclosed by the carpel walls. 

There are several rows of stamens encircling the pistils. Each 
stamen or microsporophyl bears four elongated, parallel, sporangia con- 
taining pollen or microspores. The stalk of the stamen is called the 
filament, while the four pollen-sacs (sporangia) are known collectively 

A. Different kinds of pollen grains, highly magnified, two 
of them forming tubes. (After Duggar.) 

B, C. Parts of a stamen. 

A, front; B, back; a, anther; c, connective; /, filament. 
(After Strasburger.) 

D, E, F, Modes of discharging pollen. 

A, by longitudinal slits in the anther cells (amaryllis) ; B, 
by uplifting valves (barberry) ; C, by a pore at the top of each 
anther lobe (nightshade). (After Baillon.) 

as the anther. When mature, the sporangia split longitudinally and 
permit the escape of the pollen. 

There are two series of leaf-like structures below the structures we 
have just been discussing. These two series together form the perianth. 

Plant World Continued 


The upper series is made up of yellow petals. The petals collectively 
form the corolla. The lower series consists of five pointed, green sepals, 
and collectively forms the calyx. 

A spore-mother-cell, or archespore, arises in the ovule (Fig. 148A). 
This then divides into four young megaspores, only the deeper one de- 
veloping. The other three perish. There is thus only a single megaspore 
in the ovule. The nucleus of the megaspore later divides into two, each 
portion moving toward opposite poles of the megaspore cavity. Each 
of these portions divides twice, thus forming four nuclei at each pole. 

One nucleus from each pole (often called the polar nuclei) then 
moves toward the center and these two meeting, unite. 

One of the nuclei about the pole functions as an egg nucleus. The 
two companion cells are called synergids. The cells at the opposite pole 
are called the antipodal cells. 

It is at this time that the pollen, which has fallen on the carpel 

f>0 Stig 

Fig. 148. 

A. At the left, diagram of the anatomy of an angiospermous flower shortly- 
after pollination; anth., anther; fil., filament; st., stamen; siig., stigma; p. g., 
pollen grains germinating; sty., style; pt., pollen tube; o. w., ovary wall; o., ovule, 
containing embryo-sac; pet., petal; sep., sepal. 1-8, Stages in the development of 
the female gametophyte_ (embryo-sac); meg.sp., megaspore-mother-cell ; i.i., inner 
integument; o.i., outer integument; fun., funiculus; dial., chalaza; mi., nucellus 
(megasporangium) ; emb., embryo-sac. All diagrammatic. (From C. Stuart 
Gager's "Fundamentals of Botany," by permission of P. Blaki'ston's Son & Co., 

B. Diagrammatic Representation of Fertilization of an Ovule. 

i, inner coating of megasporangium (ovule); o, outer coating of ovule; p, 
pollen tube proceeding from one of the pollen grains on the stigma; c, the place 
where the two coats of the ovule blend. (The kind of ovule here shown is inverted, 
its opening m being at the bottom, and the stalk / adhering along one side of the 
ovule.) a to e, embryo sac, full of protoplasm; a, so-called antipodal cells of 
embryo sac; n, central nucleus of the embryo sac; e, nucleated cells, one of which, 
the egg cell, receives the male nucleus of the pollen tube; /, funiculus or stalk of 
ovule; m, micropyle or opening into the ovule. — (After Luerssen.) 


General Biology 

stigma, germinates to produce a reduced gametophyte and a pollen tube. 
This pollen tube penetrates the soft stigma tissues and carries two sperm 
toward the ovary cavity. As the pollen tube reaches the ovule, it enters 
a tiny pore, called the micropyle, between the two integuments, and 
then passes through the nucellus. The ovule is thus penetrated, and 
one of the sperm unites with the egg and fertilizes it. 

The zygote now divides continually, and soon there is developed a 


<T A 

Fig. 149. Diagram of Life-cycle of an Angiosperm (Alisma 

9, female gametophyte (embryo-sac) ; 8a and 9a, male gameto- 
phyte (pollen-grain). (After J. H. Schaffner.) 


wAJl, |v!auuu£ of 
*X»ml»\, uvuuu. auwui 

Fig. ISO. 
Development of the pea fruit from the pea flower. 
Yung's Chart.) 


tiny stem with a little root at one end and two rudimentary leaves at 
the other. 

The gametophyte has, in the meantime, resumed its development, 
due to the union of the second sperm nucleus with the two polar nuclei, 
to form the endosperm nucleus. This endosperm nucleus divides 
rapidly, although the cell walls are much delayed in this development. 

Plant World Continued 


In a short time the endosperm has surrounded the embryo sporophyte 
and has filled in the growing ovule. This surrounding and nourishing 
cell mass is now called the endosperm, which is neither gametophyte 
nor sporophyte. 

As the ovule grows in size, its outer coat becomes thickened and 
hardened, and the endosperm within enlarges and solidifies. A layer 
of cells at the base of the ovule now becomes corky and checks the 
supply of water, so that the whole ovule becomes hardened to form the 

It will be noted, therefore, that the spermatophytes also show an 
alternation of generations, the ordinary plant being the sexless type. It 

is this ordinary flowering plant 
which produces the microspores, or 
pollen grains, and megaspores. In 
the nuclear divisions which produce 
these cells, the chromosome number 
is reduced to half the original num- 

The pollen grains produce one 
of the sexual phases of the life his- 
tory, the male gametophyte, which 
forms the sperm nuclei ; the mega- 
spore produces the other sexual 
phase, the female gametophyte 
which bears an egg. Fertilization 
occurs by the fusion of a sperm cell with the egg; thus the nucleus of 
the fertilized egg contains twice the number of the reduced amount of 
chromosomes, one-half of which has been contributed by the sperm and 
one-half by the egg. The fertilized egg develops into the embryo of the 
seed which, upon germination, becomes the mature sporophyte or sexless 
phase of the life history with its characteristic number of chromosomes. 

References : 

Strasburger, Noll, Schenck and Karsten, "A Textbook of Botany." 

Coulter and Chamberlain, "Textbook of Botany." Vols. I and II. 

Coulter, "Plant Structures." 

Wm. C. Stevens, "Plant Anatomy." 

C. W. Ballard, "The Elements of Vegetable Histology." 

C. S. Gager, "Fundamentals of Botany." 

Berger and Davis, "Principles of Botany." 

C. E. and E. A. Bessey, "Essentials of College Botany." 

Edson S. Bastin, "College Botany." 

Geo. Massee, "A Textbook of Fungi." 

F. L. Stevens, "The Fungi which Cause Plant Disease." 

Elizabeth M. Dunham, "How to Know the Mosses." 

Wm. N. Clute, "The Fern Allies." 

Fig. 151. 
Median section of the flower of a Butter- 
cup showing its constitutent parts. On the 
outside (lowest down in the figure and shaded) 
are the sepals of the calyx: within this the 
large petals of the corolla of which three are 
shown; within this and seated higher on the 
axis are the numerous club-shaped stamens, 
each of which bears four pollen-sacs. Cen- 
trally in the flower are the numerous carpels, 
one of which is dissected so as to show its 
single ovule, or future seed. (From Bower 
after Le Maout and Decaisne.) 



THE Coelenterata (Gr. koilos=hollow-|-enteron=intestine) are all 
aquatic (mostly marine) animals, possessing a single system of 
internal chambers, called a gastro-vascular-cavity. This cavity 
has a single opening which serves both as a mouth and a vent for eges- 
tion and excretion. In other words, digestion and circulation all occur 
in this single tubular cavity. In all the higher forms of animal life 
there is a coelom ( ), that is, a cavity between the 

intestinal tract and the body wall. This was observed in the frog where 
all the viscera ( ) are inside the body but outside 

the intestinal tract. 

In the Coelenterata, there is a radial symmetry as contradistin- 
guished from the bilateral symmetry of the frog. 

The animals belonging to this phylum are diploblastic, that is, they 
have gone through the gastrula stage in developing and remained sta- 
tionary at the end of that stage, with this exception, that they just begin 
forming a third layer which, however, never becomes a regular tissue. 
The entoderm and ectoderm are separated from each other by a thick 
mucilaginous mesoglea ( ) or mesenchyme 

( ). The point of value here is that, in the higher 

forms, this midlayer becomes an actual tissue by forming a very definite 
sheet of cells, called the mesoderm, while in the Coelenterata the layer 
does not become cellular. The midlayer here acts as though it were 
about to form into a tripoblastic animal, but has not succeeded. 

A few migratory cells may be found in the mesoglea, but as a whole 
it is non-cellular. 

The phylum is further distinguished by the fact that, in practically 
all its members, there are stinging cells [sometimes called nettle-cells 
or nematocysts ( )]. 

Nerve cells (sensory) and muscle cells both occur. 

Reproduction by non-sexual methods is the more common, though 
sexual methods may alternate with non-sexual to form individuals of 
quite unlike appearance. 


The classic coelenterate for laboratory study is this little animal 
(Fig. 152), found in ponds and streams attached by its basal end to 
various types of aquatic vegetation. It is from 2 to 20 mm. long; con- 
sequently it can be seen by the naked eye. 

The entoderm contains the brown bodies from which the animal 
receives its name. The animal itself has a mouth opposite the basal disk. 

The Coelenterata 


About the mouth, there is a varying number of tentacles, usually four 
to seven. Th^se are closed at their free ends, but their interior channels 
are a direct continuation of the gastro-vascular cavity. 

At the distal third of the body, the male gonads, the testes, are seen 
as cone-shaped elevations during the breeding season (September and 
October), while the female gonads, the ovaries, are knoblike projections 

close to the basal disk. In addition 
to these sexual organs, one may find 
buds on various parts of the body. 

The Hydra is a diploblastic 
animal, that is, one which has re- 
mained in the gastrula stage. This 
means that the simple indentation 
of the original blastula has given the 
animal only epithelial tissue, for 
epithelium is surface tissue, and 
both inner and outer portions of this 
animal are surface tissues. 

The ectoderm is primarily pro- 
tective and sensory, and is made up 
of two principal kinds of cells: (1) 
epitheliomuscular, and (2) inter- 
stitial. The former are shaped like 
inverted cones, and possess long (up 
to .38 mm.), unstriped contractile 
fibrils at their inner ends. These 
enable the animal to expand and 

The interstitial cells lie among 
the bases of the epitheliomuscular 
cells. They give rise to three kinds 
of nematocysts or stinging cells 
(Fig. 153). Nematocysts are present on all parts of the body, except the 
basal disc, and are most numerous on the tentacles. The interstitial cell, 
in which the nematocyst develops, is called a cnidoblast ( ). 

It contains a nucleus and develops a trigger-like process, the cnidocil 
( ), at its outer end, but is almost completely filled 

by the pear-shaped nematocyst. Within this structure is an inverted, 
coiled, thread-like tube with barbs at the base. When the nematocyst 
explodes, this tube turns rapidly inside out and is able to penetrate the 
tissues of other animals. The explosion is probably due to internal 
pressure produced by osmosis, and may be brought about by various 
methods such as the application of a little acetic acid or methyl green. 
Many animals when "shot" by nematocysts are immediately paralyzed 
and sometimes killed by a poison called hypnotoxin which is spread by 
the tube. 


A, an animal in its expanded form; B, 
the same animal contracted; C, a diagram of 
the longitudinal section of the animal, show- 
ing the internal structure; D, an epithelio- 
muscle cell; E, a bit of the body wall highly 
magnified showing the two layers of the body; 
F, a digestive cell; G, one of the nemato- 
cysts with its thread extruded; H, a second 
type of nematocyst with the coiled thread 
within the sac; I, nematocyst of the third 
type with its thread extruded; /, a bit of the 
tentacle, very highly magnified, showing the 
batteries of the nematocysts; K, two of the 
secreting cells of the basal disk, en, cnidocil; 
cc, ectoderm; en, endoderm; m, mouth; mes, 
mesogloea; o, ovary; s, spermary; t, new ten- 
tacle forming. (After Conn.) 


General Biology 

Two kinds of nematocysts, smaller than those just described, are 
also found in the ectoderm of Hydra. One of these is cylindrical and 
contains a barbless thread which, when discharged, aids in the capture 
of prey by coiling around the spines or other structures that may be 

Certain ectoderm cells of the basal disk of Hydra are glandular and 
secrete a sticky substance for the attachment of the animal. 

The entoderm, the inner layer of cells, is primarily digestive, ab- 
sorptive, and secretory. The digestive cells are large, with muscle fibrils 
at their base, and flagella, or pseudo- 
podia, at the end which projects into 
the gastrovascular cavity. The flagella 
create currents in the gastrovascular 
fluid, and the pseudopodia capture solid 
food particles. The glandular cells 
are small and without muscle fibrils. 
Interstitial cells are found lying at the 
base of the other entoderm cells. 

ectoderm cell 

- interstitial cells 




-food granule, Fig - 154 - 

Hydra moving like a measuring worm and 
using tentacles as feet. (From Jennings, after 

Fig. 153. Transverse Section of Hydra fusca. Wagner.) 
(After Shipley and MacBride.) 

The mesoglea is an extremely thin layer of jelly-like substance 
situated between the other two layers. 

From recent investigations it seems well established that Hydra 
possesses a nervous system, though complicated staining methods are 
necessary to make it visible. In the ectoderm there is a sort of plexus 
of nerve-cells connected by nerve-fibers with centers in the region of 
the mouth and foot. Sensory cells in the surface layer of cells serve as 
external organs of stimulation, and are in direct continuity with fibers 
from the nerve cells.- Some of the nerve-cells send processes to the 
muscle fibers of the epitheliomuscular cells, and are, therefore, motor 
in function. No processes from the nerve-cells to the nematocysts 
have yet been discovered, though they probably occur. The entoderm 
of the body also contains nerve-cells, but not so many as are present in 
the ectoderm. 

The Coelenterata 251 

Hydra obtains its food by throwing out nematocysts and paralyzing 
its prey. The surface of the tentacle itself is somewhat sticky, which 
assists in keeping food from getting away, once the tentacle bends about 
it and carries it to the animal's mouth. After the food enters the mouth, 
the forepart of the animal contracts to send it downward. 

There are gland-cells in the entoderm which secrete a digestive 
fluid, and it is probable that some digestion takes place in the entoderm 
cells themselves. These latter have little flagella by which food is 
whipped about. When digestion takes place within these entoderm cells, 
digestion is said to be intracellular. 

It is interesting to note that Hydra will not respond to food stimuli 
or capture prey after being fed. 

The normal position of Hydra is an attachment to some solid object 
by its basal disk. When the animal moves from one attached place 
to another, it uses its tentacles as feet, slowly moving them along as 
though walking upon them, and when a suitable location has been 
found, releasing its body at the basal end and attaching it to the newly- 
found spot. (Fig. 154.) 

The reproduction of Hydra is especially interesting in that it fur- 
nishes us with excellent proof for Weismann's insistence on the separa- 
tion of somatoplasm and germ-plasm. 

This animal usually reproduces by budding, as does yeast, except 
that the bud in this instance pushes out and becomes stalk-shaped. The 
tentacles of the bud grow from the distal end of the new stalk bud, and 
the entire new organism is pinched off from the mother stalk or body. 
(Fig. 152, C.) _ 

In fact, it is not uncommon for one of these buds to form new buds 
on its body before it is ready for independent existence itself. At all 
times, the cavity of the newly forming animal is in direct continuation 
with the mother cavity, until the pinching-off process occurs. 

There is a division of the body sometimes, though very infrequently, 
by simple fission ( ), that is, by a splitting of the 

entire animal lengthwise, commencing from the distal end and extending 
to the basal disk. Sometimes, also, even the buds reproduce in this 
manner, while transverse fission is not unknown. 

In the sexual method, the spermatozoa from the testes escape into 
the surrounding water. The eggs arise in the ovary from ectodermal 
interstitial cells. Usually only one egg in the ovary grows to maturity, 
though several may begin growth, only to have one of them — the 
stronger by virtue of position, or ability to obtain more food — absorbing 
the others. Two polar bodies are given off from this egg when it is 
ready for fertilization, and then it is said to be mature. 

The cleavage of the egg is total, and almost equal. After this origi- 
nal egg has divided several times, the blastula is formed with a cavity 
called the blastocoel ( ). Cells from the inner 

portion bud off and make a sort of solid gastrula-like structure; this 


General Biology 

later becomes the entoderm. The ectoderm then secretes a thick 
chitinous ( ) shell covered with sharp projections, 

after which the embryo separates from its parent and falls to the bottom 
of the disk in which it is placed. Here it remains unchanged for several 
weeks. Interstitial cells then make their appearance followed by an- 
other resting period, after which the outer chitinous envelope breaks 
away and the elongation of the escaped embryo continues. Mesoglea 
is now secreted by the ectoderm and entoderm cells. A circlet of tentacles 
arises at one end, and a mouth appears in their midst. The young Hydra 
thus formed soon grows into the adult condition. Almost any part of 
the Hydra may be cut off, and each part will grow into a complete new 
animal. This is supposed to be due to the fact that Hydra is an animal 
composed of tissues which have not yet become organs as in the higher 
animals. Therefore, the original germ-cells have not divided so often 
as in higher animals, and each cell contains a little portion of germ- 
plasm which causes each cell to have the power or potentiality of pro- 
ducing a complete organism. This theory receives additional weight 
from the fact that the Hydra can and does reproduce in practically every 
known way : sexual, asexual, by budding, by longitudinal and transverse 
fission, in addition to having the ability of restoring any lost part, and 
of forming a complete new animal from the smallest part. 

When, however, an animal is classified in one of the higher phyla 
and its somatoplasm is, therefore, further removed from the germplasm, 
the regenerative ability decreases. This is shown in man, where a piece 
tet of skin, when removed, will 

be replaced, though an entire 
finger will not. 

Regeneration means that 
a part of an organism can 
reproduce the whole or at 
least a portion of the lost 
part. Regeneration is to be 
distinguished from repro- 
duction, though in Hydra 
the two are intimately re- 

As has been stated, there 
is an alternation of genera- 
tions in Hydra. The form we have been discussing so far, is called the 
Hydroid form or the polyp ( . ), while the asexual 

form, so different in appearance from the hydroid, is umbrella shaped 
and is called a medusa ( ) (Fig. 155). The convex 

portion is usually the upper surface. Tentacles hang down from the 
edges. At first glance the two forms appear totally dissimilar, but with' 
a clear conception of what a gastrula really is, we can readily imagine 
grasping the hydroid form by the mouth and pushing this portion of the 

Fig. 155. Medusa, showing gastrula-form. 

Diagrams showing the similarities of a polyp (A) 
and a medusa (B). circ, circular canal; ect, ectoderm; 
end, entoderm; ent. cav, gastrovascular cavity; hyp, 
hypostome; mnb, manubrium; msgl, mesoglea; mth, 
mouth; nv, nerve rings; rad, radial canal; v, velum. 
(From Parker and Haswell.) 

The Coelenterata 


animal in upon itself, when we have the gastrula still, and also the 
medusoid form. 

It must be remembered that some species may always retain the 
medusoid form and others the hydroid, while still a third may alternate 
regularly or irregularly between the two. 


This is a colonial form of Hydra found attached to rocks, wharves, 
and to various algae. New individuals form by budding, but the newly- 
formed animals remained attached to the parent stalks. (Fig. 156.) 

Such a colony consists of a basal stem, the hydrorhiza ( ), 

which is attached to the substratum. At intervals, upright branches, 
known as hydrocauli ( ), are given off. At every 

bend in the hydrocaulus, a branch arises. The stem of this side-branch 

Fig. 156. Hydrozoa. 

A, part of a colonial Hydrozoan, Obelia. B, Longitudinal sec- 
tion through a single hydranth. C, Cross section through medusoid 
individual. 1, ectoderm; 2, entoderm; 3, mouth; 4, coelenteron; 5, 
coenosarc; 6, perisarc; 7, hydrotheca; 8, blastostyle; 9, medusa- 
bud; 10, gonotheca; or.c, mouth region; end. and endt., entoderm; 
ect., ectoderm; st.L, mesoglea lying between ectoderm and ento- 
derm; hyth, hydrotheca. (From Borradaile after various authors.) 

is ringed and expanded at the end into a hydra-like structure, the 
hydranth ( ). Each individual polyp consists of a 

hydranth and the part of the stalk between the hydranth and the point 
of origin of the preceding branch. Full-grown colonies usually bear 
reproductive members (gonangia) in the angles where the hydranths 
arise from the hydrocaulus. 

All of the soft parts of the Obelia colony are protected by a chitinous 


General Biology 

covering, called the perisarc ( ), which is ringed at 

various places, and expanded into gonothecae and cup-shaped hydro- 
thecae ( ) to accommodate the hydranths. 

A shell extends across the base of the hydrothecae which serves to 
support the hydranth. The soft parts of the hydrocaulus and of the 
stalks of the hydranths constitute the coenosarc ( ) 

and are attached to the perisarc by minute projections. The coenosarcal 
cavities of the hydrocaulus open into those of the branches and thence 
into the hydranths, producing in this way a common gastro-vascular 

The coenosarc consists of two layers of cells — an outer layer, the 
ectoderm, and an inner layer, the entoderm. These layers are continued 
into the hydranth. The mouth is situated in the center of the large 
knob-like hypostome ( ) and the tentacles ( ), 

about thirty in number, are arranged around the base of the hypostome 
in a single circle. Each tentacle is solid and consists of an outer layer 
of ectodermal cells and a single axial row of entodermal cells with a 
large number of nematocysts at the extremity. The hydranth captures, 
ingests, and digests food just as does Hydra. 

The reproductive organs develop quite like the hydranths, as buds 
from the hydrocaulus. They thus represent modified hydranths. The 
central axis of each is called a blastostyle ( ), and, 

together with the gonothecal covering, is known as the gonangium 
( ). The blastostyle gives rise to medusa-buds 

which soon become detached and pass out of the gonotheca through the 
opening in the distal end. 

Some medusae produce eggs, and others, sperm. The fertilized eggs 
again develop into colonies like those which gave 
rise to the medusae. The medusae provide for the 
dispersal of the species, since they swim about in 
the water and establish colonies in new habitats. 
The medusae of Obelia are shaped like an umbrella 
with a fringe of tentacles and a number of organs 
of equilibrium on the edge. Hanging down from 
the center is the manubrium 
( ) with the 

mouth at the end. The gastro- 
vascular cavity extends out from the 
cavity of the manubrium into four 
radial canals on which are situated 
the reproductive organs. 

The germ-cells of the medusae 
of Obelia, after arising in the ecto- 
derm of the manubrium, migrate 
along the radial canals to the repro- 
ductive organs. When mature, they 

A. B. 

Fig. 157. 

A. Liriope Exigua (family Geryoniidae). 

B. Hydralike stage in the development of 
Gonionemus. One of the tentacles is carrying 
a worm (w) to the mouth. Tentacles in con- 
tracted state. (From the Cambridge Natural 
History, after Perkins.) 

The Coelenterata 255 

break out into the water. The eggs are fertilized by spermatozoa which 
have escaped from other medusae. Cleavage is similar to that of Hydra, 
and a hollow blastula and solid gastrula-like structure are formed. The 
gastrula-like structure soon becomes ciliated and elongates into a free- 
swimming larva called a planula ( ) which soon 
acquires a central cavity and becomes fixed to some object. This then 
forms a new colony. 

When there is an alternation of generations, one sexual, reproducing 
by eggs and spermatozoa, and the other asexual, reproducing by division 
or budding, such an alternation of generations is called metagenesis 

( )• 

In Obelia the asexual generation (the colony of polyps) forms buds 
of two kinds, the hydranths and the gonangia ( ). The 

sexual generation (the medusoid) reproduces only by eggs and sper- 

Hydra have no regular medusoid stage, and Geryonia (Fig. 157A), 
( ), no polyp, or hydroid, stage. 

Gonionemus (Fig. 157B) ( ) 

The structure of a medusa, or hydrozoan jellyfish, is well illustrated 
by Gonionemus, which is quite common along the eastern coast of the 
United States. It is about half an inch in diameter. In general form 
it is similar to the medusa of Obelia. The convex or aboral surface is 
called the exumbrella ( ), and the concave, or oral 

surface, the subumbrella ( ). The subumbrella is 

partly closed by a perforated membrane called the velum ( ). 

The animal takes water into the subumbrella-cavity, and then forces it 
out through the central opening in the velum by contracting its body, 
thus propelling itself in the opposite direction. This method of locomo- 
tion is called hydraulic. It is common to all medusae. 

The tentacles (from sixteen to about eighty in number) are capable 
of great contraction. Adhesive or suctorial pads are found near their 
tips. Hanging down into the subumbrellar cavity is the manubrium 
with the mouth at its end surrounded by four frilled oral lobes. The 
mouth opens into a gastrovascular cavity which consists of a central 
"stomach" and four radial canals. The radial canals enter a circum- 
ferential canal which lies near the margin of the umbrella. 

The cellular structure of Gonionemus is similar to that of Hydra, 
but the mesoglea is thicker and gives the animal a jelly-like consistency. 
Then there are many nerve cells scattered about beneath the ectoderm, 
and a nerve ring is placed about the velum. There are sensory cells 
with a tactile function on the tentacles. At the margin of the umbrella 
there are two kinds of sense organs: (1) Those at the base of the 
tentacles are round bodies containing pigmented entoderm cells and 
communicate with the circumferential canal. (2) Those between the 
bases of the tentacles are small outgrowths, probably organs of equi- 


General Biology 

librium, that is, statocysts ( ). Muscle fibers are 

present in both exumbrella and subumbrella. 

Beneath the radial canals the sinuously folded reproductive organs, 
or gonads, are suspended. Gonionemus is dioecious ( ), 

each individual producing either eggs or spermatozoa. These repro- 
ductive cells break out directly into the water, where fertilization takes 
place. A ciliated planula develops from the egg as in Obelia. This soon 
becomes fixed to some object and a mouth appears at the unattached 
end. Then four tentacles grow out around the mouth, and the hydra- 
like larva is able to feed. Other similar hydra-like larvae bud from its 
walls. How the medusae arise from these larvae is not known, but 
probably there is a direct change from the hydroid form to the medusa. 


Whenever there is a division of labor among the different members 
of the same colony so that each does a particular work, such colony is 
said to be polymorphic ( ) if there are more than 

two kinds of specialized individuals ; dimorphic, if only two different 
specializations have taken place. 

The "Portuguese man-of-war" 
(Fig. 158) is an excellent example 
of the former, in that it is a bladder- 
like structure to which many tenta- 
cles are attached. It floats upon the 
water. Some of these tentacles 
are nutritive, others are tactile 
( ), some contain 

batteries of nematocysts, others are 
male reproductive zooids, and still 
others give rise to egg-producing 

The Coelenterata (together with 
the Echinoderma) were formerly 
called Radiata on account of their 
radial form. It is now known that 
in the higher groups of coelenterates, 
this radial form may be transformed 
into a b i r a d i a 1 or bilateral sym- 

Older writers often spoke of the 
coelenterates as Zoophyta (animal- 
plants) on account of their resem- 
blance to plants both in appearance 
and in their method of attachment. 
Then, too, these animals simulate 

Fig. 158. 

A, Physalia or Portuguese man-of-war, a 
colonial Hydrozoon. (From Hegner, after 

B, Diagram showing possible modifica- 
tions of medusoids and hydroids of a hydro- 
zoan colony of the order Siphonophora. c. gas- 
trozooid with branched, grappling tentacle, f; 
g, dactylozooid with attached tentacle, h; i, 
generative medusoid; k, nectophores (swim- 
ming bells) ; /, hydrophyllium (covering 
piece); m, stem of corm; n, pneumatophore. 
The thick black line represents entoderm, the 
thinner line ectoderm. (From Hegner after 

The Coelenterata 


Fig. 159. Scyphozoa. 

A, Tessera prince ps, order Stauromedusae. 

B, Periphylla hyacinthia, order Peromedusae. 

C, Charybdea marsupialis, order Cubomedusae. 
G, gonads; Gf, gastral filaments; ov, gonads; 
Rf, annular groove; Rk, marginal bodies; Rm. 
circular muscle; T, tentacles. (From Sedgwick, 
after Haeckel.) 

Fig. 160. Examples of Alcyonoria. 

Coral. A, Tubipora musica, organ-pipe 
:oral, a young colony. Hp, connecting hori- 
zontal platforms; p, skeletal tubes of the 
zooids; St, the basal stolon. B, Alcyonium 
iigitatum, with some zooids expanded. C, 
Corallium, a branch of precious coral. P, 
oolyp. D, Pennatula sulcata, a sea-feather. 
(A and B, from Cambridge Natural History; 
C, from Sedgwick, after Lacaze Duthiers; D, 
from Sedgwick, after Kolliker.) 

plant-conditions by their method of reproduction, namely, by fission and 
budding, as well as by forming colonies. 


There are three great classes of coelenterates — Hydrozoa 
( ), Scyphozoa ( ), and 

Anthozoa ( ). 

The Hydrozoa possess neither stomodaeum nor mesenteries 
( ), and their sex-cells are discharged directly to 

the exterior. Hydra and Obelia belong to this class. 

The Scyphozoa may, or may not, possess a stomodaeum and mesen- 
teries. The stomodaeum is more or less equivalent to the gullet in 
coelenterates, serving as the passageway between mouth and the gastro- 
vascular cavity or "stomach." The membranes, which hold this stomo- 
daeum in place, are called mesenteries. 

The position of tentacles and tentaculocysts is made use of in sepa- 
rating the coelenterates into the various classes. 

Examples of Scyphozoa (Fig. 159) are: Tessera, order Stauro- 
medusae; Periphylla, order Peromedusae; and Charybdea, order Cubo- 

The Anthozoa are divided into two sub-classes as follows : 

Sub-class I. Alcyonaria (Fig. 160), all of which have eight hollow, 
pinnate, tentacles and eight complete mesenteries. They also possess 
one siphonoglyphe, which is ventral in position, while all the retractor 
muscles of the mesenteries lie on the side toward the siphonoglyphe 

( )• 


General Biology 

A. B. 

Fig. 161. Examples of Zoantharia. 

A, Oculina speciosa, a branch of madreporarian coral. 

B, Meandrina, a rose-coral of the order Madreporaria. 

C, A group of sea anemones. (After Andres.) 

(After Sedgwick.) 
(After Weysse.) 

Examples of Alcyonaria are the organ-pipe coral, known as 
Tubipora, of the order Stolonifera, and the pretty sea-fans and the red 
coral used in jewelry. The latter is known as Corallium of the order 

Sub-class II. Zoantharia (Fig. 161). These usually possess many 
simple, hollow tentacles, generally arranged in multiples of five or six. 
There are two siphonoglyphes as a rule, and the mesenteries vary in 
number. The retractor muscles are never arranged as in the Alcyonaria. 
A skeleton may or may not be present. The animals may be simple or 

Examples of Zoantharia are the sea-anemones such as Actiniaria, 
and the stony corals such as Oculina of the order Madreporaria, and the 
rose-coral Meandrina, order Madreporaria. 



FROM what has already been learned, it is known that animals may 
■ be divided, according to whether or not they have a backbone, 
into great groups — the vertebrates and the invertebrates. Also, 
division may be made according to whether they are composed of one 
or more cells into protozoa and metazoa. The latter division may again 
be subdivided according to the number of germ layers each form 
develops, into diploblastic and triploblastic organisms. 

Now we come to another common method of classifying animals into 
two groups — the coelomata and the acoelomata. 

With the exception of the frog, all animals studied so far — the 
Protozoa and Coelenterata — belong to the acoelomata, because they have 
no additional cavity between the digestive tract and the body wall. 
Coelomata have such a body-cavity. All animals higher in the scale of 
life than hydra are coelomates. 

It will be remembered that in hydra there was a thick mucilaginous 
substance — the mesoglea — formed between the ectoderm and entoderm. 
In some of the lower forms of acoelomata there are processes stretching 
across from inner to outer germ-layer, which often secrete fibers which 
become connective tissue or even muscular fibers. Where the cells and 
fibers are sparse the space is called a primary body-cavity. Where they 
are abundant, there is a tissue called parenchyma ( ) 

or connective tissue. 

This body cavity, also known as the coelomic cavity (Fig. 162) or 
coelom (Gr. koiloma=a thing hollowed out), consists of one or more 
pairs of sacs with perfectly defined walls lying at the sides of the ento- 
dermic tube. In the adult these sacs join above and below the entoderm, 
while the adjacent walls entirely or partly break down to form one 
continuous cavity. The wall of the coelom and the tissues derived from 
it are mesoderm. 

The distinctive difference between the primary body cavity of the 
coelenterates and this secondary body-cavity of the coelomates, is a dif- 
ference in the walls of the cavities and not in the space between the 
walls. The outer wall of the primary body cavity is merely ectoderm. 

It will be remembered that this primary body-cavity serves both as 
a digestive and circulatory system in the coelenterates. In the higher 
animals, therefore, it may be said that the blood-vessels are really part 
of the primary body-cavity. 

In triploblastic animals the mesoderm does not form a completely 
solid mass extending the entire length of the body. A slight cavity is 
left in its center along the long axis of the organism. 


General Biology 

This mesoderm forms in two ways: either (1) by little pouches 
growing from the entoderm which are then nipped off, or (2) by two 
large cells which grow as buds from the entoderm, and which, when 
once formed, grow rapidly, forming the so-called mesodermic bands. 
These bands later become hollowed out. The two cells which form the 
original bud, are termed pole-cells. This hollowed out portion is the 
coelom. A close study of Figure 163 will make a better understanding 
of the above possible. 

It must be understood that both these methods of mesoderm forma- 
tion are not likely to be found in any one animal. 

The open space thus formed, which we have called the coelom, has 
thus a layer toward the outside of the body and a layer of cells, or wall, 
toward the entoderm from which it sprang. The outer wall of the coelom 
is called the somatic layer or the somatopleure ( ), 

while the inner is known as the splanchnopleure ( ). 


Dorsal vessel 

Circular muscle 





flayer of 
chlorogogen colls 



Veniral vessel 
K Submural vessel 

Eig. 162. 

Transverse section through the middle region of the body 
of the earthworm, Lumbricus. (From Parker and Haswell, 
after Marshall and Hurst.) 

Fig. 163. 

Two stages in the early develop- 
ment of a common fresh-water mol- 
lusc, Planorbis, to show the origin 
of the mesoderm cells. 

The ectoderm cells are deeply 
shaded, the endoderm cells _ are un- 
shaded. A. Young stage in which 
the endoderm has not begun to be 
invaginated; it is a lateral optical 
section. B. Older stage, optical sec- 
tion seen in front view; the endo- 
derm cells are invaginating, and the 
two mesoderm cells are seen on each 
side. 1. Mesoderm or pole-cells; in 
B, each has budded off another meso- 
derm cell. (After Rabl.) 

When pole-cells form, the cavity of the digestive canal is small in 
proportion to the thickness of its wall, so that the pole-cell may be con- 
sidered as "a solid pouch." 

In most Coelomata the mesoderm, or coelomic wall, forms by far 
the greater portion of the body. There are sometimes cells which form 
in the primary body-cavity, to which some writers have also applied the 
term mesoderm. This term should, however, be reserved for the walls 
of the coelom as just described, while mesenchyme ( ) 

should be used for the cells forming within the primary body-cavity. 

Introduction to the Coelomata 261 

Mesenchyme arises from different germ-layers in different phyla of 
animals. It may arise from the entoderm or ectoderm or both, or even 
from the walls of the coelom. In this latter case it may spring from 
ectoderm, entoderm, and mesoderm. In the higher Coelomata it arises, 
however, partly from the ectoderm but chiefly from the outer wall of 
the coelom. Everywhere it gives rise to connective tissue and to the 
tissues developed from this (tendon, cartilage, bone, etc.), whereas the 
coelomic wall, or true mesoderm, gives rise to the generative cells and 
their ducts, and the main parts of the muscular system, including the 
muscular coats of the principal blood-vessels. 

The entoderm, after the mesoderm has separated from it, forms the 
lining of the digestive tube and of its appendages, which in the higher 
vertebrata are such organs as the lungs, liver, pancreas, and urinary blad- 
der. The basis of the skeleton of vertebrata, the gelatinous rod called the 
notochord, also arises from the entoderm. 

After gastrulation has taken place in the growing embryo, there are 
only two germ layers, ectoderm and entoderm. The inner layer under- 
goes various changes, as it is to be used for 
a totally different purpose from .its outer, 
protective layer. It must be remembered, 
however, that just after indentation, both 
" ^wausitsr layers are alike in that they have both con- 

Diagrammatic cross section of the stituted the simple blastula. The blastula, 
h y Sa)° £ id^rrSdSSS."^ * will be remembered, is but a single layer 
latter forms a tube within a tube. of cells forming a more or less spherical 

body. The opening formed by gastrulation, and known as the mouth or 
stomodeurn ( ), does not undergo the same change 

that does the part on the more interior portion of what is now called the 
entoderm. In fact, the mouth region remains ectodermal. As soon as 
an organism has formed three germ-layers and has both an opening 
in its body for ingestion as well as egestion of food, there comes 
another infolding of ectoderm in the gastrula at the opposite end from 
the stomodeurn. This forms an anal opening which is called a procto- 
deum ( ). This infolding, just as the stomodeal 
infolding, is also ectoderm. 

It is of interest and value here to know that the entire brain and 
nervous system arise from ectoderm. It will be readily understood why 
this is so, when it is realized that no organism from the simplest flower 
up to man, could possibly live unless there were some method by which 
such organism could protect itself when danger threatened. Any 
mechanical injury, such as pressure or laceration, cannot affect the body 
unless it strikes the outer portions first. Therefore, the sensory nerve 
endings must be placed close to the outer portion of the body so that 
they can receive the message of threatened danger first. These danger 
messages are then carried to the central nervous system where a coordi- 
tion must be brought about between the sensory fibers and the motor 

262 General Biology 

nerves, thus making it possible for any or all parts of the body to be 
withdrawn from the zone of danger. 

For toxic injuries, as well as parasitical invasions, which come 
through the intestinal tract, the student must think of the body, when 
drawn out completely, as forming a tube within a tube. (Fig. 164.) 

The inner one, called the intestinal, or digestive tract, has an open- 
ing straight through the body. This means that the inside of the diges- 
tive tract is really outside the body in so far as exterior environmental 
conditions may affect it, such as temperature, air, etc. In other words, 
it is as though one took an ordinary small gas or water pipe and placed 
it in water. There would be the same kind and quality of water on the 
inside as there would be on the outside of the pipe. 

The larger outer tube is the outer body wall. 

As the internal anatomy of the lower animals was first studied by 
physicians and others primarily interested in human anatomy, a large 
number of names is used in the description of simpler animals which are 
based on fanciful resemblances between their organs and those of man. 
Many of these names are, therefore, quite misleading. For example : 
The word stomach in the lobster denotes part of the stomodeum, while 
in the vertebrates it signifies part of the entodermic tube. The pharynx 
( ) of an earthworm is the stomodeum, while in 

fishes it includes both stomodeum and the first part of the entodermic 

Names taken from the higher animals, which are customarily used 
in the description of the alimentary canal, are as follows: Mouth or 
buccal-cavity, pharynx, oesophagus, stomach or crop, gizzard, intestine, 
and rectum. These names apply to parts succeeding one another in the 
order above given. Many biologists hold that it would perhaps be more 
logical- to sweep away altogether these and a host of similar terms em- 
ployed to designate other parts of the body, but as these terms have 
become so deeply engrained in zoological literature such a course would 
render unintelligible most of the anatomical descriptions of species we 



EARTHWORMS are found in practically all parts of the country, 
living in burrows not lower than 12 to 18 inches beneath the 
earth's surface. It is in about these depths that they find the 
richest portions of decaying vegetable and animal substances upon which 
they feed. Professor Latter has given us a most interesting account 
of these animals. During "periods of prolonged drought or frost they 
descend to greater depths and undergo aestivation ( ) 

or hibernation ( ), as the case may be, coiled up into 

a compact spiral and lying in a small excavated chamber. This is lined 
with small stones which prevent close contact with the surrounding 
earth and so permit free respiration. The sides of the burrow are kept 
moist by slime discharged from the glandular cells of the skin, and 
perhaps by liquid discharged from the body-cavity through the dorsal 
pores which occur in the grooves that separate segment from segment. 
The slime is said to possess antiseptic properties, and thus preserve the 
skin of the worm from harmful bacteria. 

"The mouth of the burrow is guarded by small stones or more 
frequently by one or more leaves pulled in to a greater or less distance. 
Fir-needles, stalks of horse-chestnut leaves and other similar things are 
often to be seen standing nearly erect upon the ground, their lower ends 
having been forcibly dragged into the mouth of a burrow by a worm. 
On still, warm nights in early autumn the rustling noise of fallen leaves 
being dragged along by worms is often plainly audible in favorable 
localities. Darwin has pointed out that worms exhibit considerable 
intelligence in drawing the narrow end of leaves of various shapes fore- 
most into the burrow : the leaves with broad bases and narrow apices 
are generally pulled in tip first, whereas when the base is narrower than 
the apex the reverse position is usually found. There is no doubt that 
worms can judge which end of any leaf is the better to seize. The 
reason for thus pulling objects into the entrance of the burrow is prob- 
ably to prevent the entry of foes, centipedes, parasitic flies, etc., to keep 
the burrow moist by preventing evaporation, to keep out the cold lower 
strata of air at night, to bring food supplies within safe reach, and also 
to enable the worms to lie near the mouth of the burrow unobserved. 
Here, however, they are not secure from all attack, for the quick ears 
of the thrush and other birds enable them to detect the slightest move- 
ment and, with a quick plunge of the beak, to seize, and after a brief 
tug-of-war, to extract the worm from its refuge. Frequently the well- 
known worm-castings are thrown up on the surface, and when this is so. 

264 General Biology 

leaves are not, as a rule, drawn into the burrows, the heap of castings 
serving the purpose. 

"The burrow is made partly by the awl-like, tapering anterior end 
pushing aside the earth on all sides, and partly by the actual swallowing 
of the earth as the worm advances, so that the animal literally eats its 
way into the soil. The organic material in the swallowed soil serves 
as food, and the residue in a state of very fine division passes out at the 
anus, and is used either to form the above mentioned castings or as a 
lining to the burrow, especially where this passes through hard, coarse 

"Perfectly healthy worms seldom leave their burrows completely 
except perhaps after a very heavy rain. The majority of those so fre- 
quently found traveling over the surface of roads and paths after rain 
are infected by the larvae of parasitic flies and doomed to die. On warm, 
moist evenings, however, worms may be seen in hundreds lying stretched 
on the surface of the ground with only the broad flattened posterior end 
remaining in the burrow. Here we see one of the uses of this modifica- 
tion in the shape of the hinder segments of the body : their greater width 
enables them to obtain a firm purchase on both sides of the burrow, and 
thus the worm is provided with a sure anchor on which it can pull, and 
at the slightest alarm, shoot back like stretched elastic into the security 
of its burrow. At other times the flat tail is employed trowelwise in 
smoothing the excrement against the walls of the burrow or in disposing 
the castings on this side and on that of the mouth of the burrow. 

"The effects produced on the surface soil by the action of earth- 
worms have been fully pointed out by Charles Darwin in his well-known 
book, 'Vegetable Mould and Earthworms.' It will be sufficient here to 
call attention to a few facts only. Worms play a most important part 
in maintaining the soil in a state suitable to vegetation. The burrows 
form ventilating tubes whereby the soil is aerated and respiration by the 
roots of plants rendered possible ; at the same time they open up drain- 
age channels, preventing the surface from becoming waterlogged. 
Doubtless also roots find an easy passage through the soil along the 
lines of burrows even after the walls have more or less fallen in. More- 
over, the excrementitious earth with which the burrows are lined is 
peculiarly suited to root fibers, being moist, loose and fertile. Micro- 
scopic examination of the earth deposited by worms shows it to resemble 
two-year-old leaf mould such as gardeners use for seed-pans and 
pricking-out young seedlings ; most of the plant-cells are destroyed, 
shreds and fragments alone remaining, discolored and friable, mingled 
with sand grains and brown organic particles. In chemical composition, 
too, worm-castings are very similar to fertile humus. 

"The castings which are thrown up on the surface materially im- 
prove the quality of the upper soil, and render it more fit for the germi- 
nation of seeds, many of which directly or indirectly get covered by the 
upturned earth. It has been reckoned that there are upwards of 50,000 

The Earthworm 265 

worms in an acre of soil of average quality: hence the total effect of 
the work of this vast host must be very considerable. Each worm ejects 
annually about 20 ounces of earth. The weights of earth thrown up in 
a single year on two separate square yards observed by Darwin were 
respectively 6.75 and 8.387 pounds, amounts which represent respectively 
14.58 tons and 18.12 tons per acre per annum. 

"In addition to this tilling action worms improve the quality of the 
soil by the leaves and other organic debris which they drag into their 
burrows, and thus bring within reach of bacteria. These, as it is well 
known, especially abound in the upper soil, and effect the speedy decom- 
position of dead animals and vegetable tissues. 

"Archaeologists are indebted to worms for the preservation of many 
ancient objects, such as coins, implements, ornaments, and even the 
floors and remains of ancient buildings that have become buried by the 
soil thrown up as worm-castings. The process of disappearance is, of 
course, hastened by the excavations effected by the worms below the 
surface, for the collapse of the burrows slowly but surely allows objects 
on the surface to sink downward. 

"In the disintegration of rocks, and the denudation of the land, 
worms play an important part. The penetration of the burrows, and 
the lining with castings, carries down the humus-acids to a considerable 
depth and exposes the underlying rocks to their solvent action. Within 
the body of the worm itself small stones and grains of sand are reduced 
to yet finer dimensions and rendered the more easy to transport by wind 
and water. On sloping surfaces the upturned castings, at first semi- 
fluid, flow down, and when dry roll down the incline, or are washed by 
the rain into the valleys and ultimately carried out to sea, while on 
level ground the dried castings are blown away to lower spots by the 
wind. The more or less parallel ridges that are frequently found on 
the sloping sides of grass-clad hills are in part, at any rate, formed by 
the material derived from worm-castings, which has temporarily lodged 
against tufts of grass, etc., and in turn furnishes a richer and deeper soil 
for stronger growth which arrests yet more and so increases the ledge. 
All land surfaces, whether level or sloping, provided they are occupied 
by worms, are reduced in altitude by their action. In no small degree, 
then, may earthworms be held responsible for our valleys and hills and 
all the softer features of our scenery." 


There are rings or segments, formed by constrictions or annuli (Fig. 
165), extending along the entire length of the animal's body. The seg- 
ments themselves are known as somites or metameres. It is from these 
ring-like (L. annulus-ring) constrictions and segments that the animals 
belonging to this group are named Annelids or Annulata. Worms are 
divided into annelids, or segmented worms, plathyhelminthes or flat 


General Biology 

worms — (Gr. platy=flat-f-helminthes— worms) ; and nemathelminthes 
or thread-worms (Gr. nema=thread+nelminthes— worms). 

The important external characteristic in the annelids is, then, a 
regional differentiation. That is, the forming of separate segments or 
regions externally, and a separation and segmentation of many internal 
„ . structures. Metamerism is com- 

mon in all higher forms of organ- 
isms except the soft-bodied animals 
such as the Molluscs and the spiny- 
skinned Echinoderms. In man this 
metamerism is distinctly shown in 
the separate segments of the spinal 

There are many differentiations 
in various regions of the earth- 
worm's body. For example, the 
anterior end is sensitive to touch 
and light to a much greater degree 
than the middle and posterior por- 
tions. On the eighth, ninth, four- 
teenth, and fifteenth segments there 
are openings of the reproductive 
system, while from the twenty- 
eighth to the thirty-seventh seg- 
ments a broad band surrounds the 
dorsal and lateral portions of the 
worm, called a clitellum, the func- 
tion of which will be explained un- 
der reproduction. 

There are from 140 to 180 seg- 
ments in the earthworm. All of the 
differentiation just mentioned occurs 
toward the anterior end of the worm. We, therefore, say that the earth- 
worm has an anterior-posterior differentiation. 

As the earthworm will always place itself in a definite position 
when crawling along— that is, will "right" itself if it be turned about, 
we speak of that portion toward the surface on which it moves as the 
ventral surface, and the surface away from this as the dorsal. If an 
animal thus rights itself, there must be a difference between the ventral 
and dorsal surfaces. This difference is spoken of as a dorso-ventral 
differentiation or dorsiventrality. 

The ventral surface will be found to be more flattened than the 
dorsal, while many little whitish glands are present toward the anterior 

Fig. 165. 

Lumbricus ter- 


Latero-ventral view of 
restris, slightly smaller than life-size 
Hatschek and Cori.) 

1. Prostomium. 2. Mouth. 3. Anus. 4. 
Opening of oviduct. 5. Opening of vas de- 
ferens. 6. Genital chaetae. 7. Lateral and 
ventral pairs of chaetae. 

XV, XXXII, and XXXVII are the 15th, 
32nd, and 37th segments. The 32nd to the 37th 
form the clitellum. (After Latter.) 

The Earthworm 267 

end. On the ventral surface are also found the mouth, anus, reproductive, 
and excretory openings, as well as peculiar bristle-like setae. These 
latter will be discussed under locomotion. 

The earthworm, like the frog, is bilaterally symmetrical. A median 
dorso-ventral line drawn through the worm divides it into two equal 
parts. This will be understood better when it is remembered that all 
unpaired parts of the animal, such as the mouth, anus, central blood 
vessel, etc., would be cut into two equal parts by a medial section, while 
all paired portions such as setae and reproductive openings would have 
one-half of such paired portion on each side of the animal. 

The dorsal excretory pores, one to each somite posterior to the 
tenth, lie in the constrictions and are difficult to find, but on the ventral 
surface various openings can readily be seen. Principally, these are two 
pairs of minute pores between the ninth and tenth and the tenth and 
eleventh somites, coming from the seminal receptacles. The male genital 
openings are on the fifteenth, and the pair of female genital openings are 
on the fourteenth somites. The excretory organs, called nephridia, have 
two openings on each somite behind the first three or four and anterior 
to the last. Practically all of the ventral openings posterior to the male 
genital pore, with the exception of the anus, are too small to be seen 
with the unaided eye. 

The animal moves along primarily by alternate rhythmic constric- 
tions of the longitudinal and circular muscles of the body-wall which 
contract and elongate successive regions of the body. There are eight 
chitinous setae to each somite, easily felt if the animal be drawn between 
the fingers. An ordinary hand-lens will show them quite clearly. There 
is then a double way in which the worm moves, the muscular action 
furnishing the contraction and expansion and the setae furnishing cog- 
like projections by which the worm can make forward progress. This 
is well exemplified by the fact that if an earthworm be placed on a 
highly polished surface, little if any progress is made by it. 

Muscles are attached to the inner parts of the setae, making it pos- 
sible to shift their positions. The flattened tail of Lumbricus terrestris, 
serves as an anchor, while the anterior portion of the animal's body lies 
on the surface of the earth. 


The earthworm illustrates a coelom (Fig. 162) as well probably as 
any form which could be given the student, for upon making either 
dorsal or ventral longitudinal incision the animal will give the appear- 
ance of a tube within a tube. The central tube is the digestive tract" 
held in its central position by little thin membranes, or walls, running 
from each outer constriction. These walls are called septa ( ) 

or dissepiments ( ). There are here, then, many 

coelomic cavities which can be clearly seen. It will be remembered 


General Biology 

that a coelom is defined as the cavity lying- between the digestive tract 
and the outer body wall. 

There are in the earthworm, muscles, nerves, glands, connective 
tissue, blood-vessels, epithelium, and endothelium, just as in the frog, 
though not developed as elaborately. There is also a delicate lifeless 
coat called the cuticle. 


The alimentary canal (Fig. 166) begins at the anterior end with a 
mouth cavity, or buccal pouch, extending from the first to the third 
somite, inclusively; the thick, muscular pharynx ( ) 

lies in somites four and five ; the oesophagus, a narrow straight tube, 

A, Longitudinal vertical section through the anterior portion of an earthworm. 
br., brain; cr., crop; fu., seminal funnel; giz., gizzard; int., intestine; n.c, nerve 
cord; neph., nephridia; oes, oesophagus; oes. gl., oesophageal gland; ph., pharynx. 
(From Parker and Haswell after Marshall and Hurst.) 

B, Section of the Alimentary Canal, c, chlorogogen cells; cm, circular muscles; 
ep, epithelium, lining the canal; Im, longitudinal muscles; v, blood vessels. (From 
Conn, modified from Sedgwick and Wilson.) 

extends through the sixth to the fourteenth somite ; a thick muscular- 
walled gizzard in somites seventeen and eighteen; and a thin-walled 
intestine from somite nineteen to the anal opening. 

The dorsal wall of the intestine is folded in, forming a longitudinal 
ridge, called the typhlosole ( ). This gives the 

intestine considerable expansion and affords additional surface for diges- 

The wall of the intestine, as in the frog, is composed of five layers. 
(Fig. 166, B) : 

(1) An inner lining of ciliated epithelium, 

(2) A vascular layer containing many small blood vessels, 

(3) A thin layer of circular muscle fibers, 

(4) A layer consisting of a very few longitudinal muscle fibers, 

(5) An outer thick coat of chlorogogen cells ( ) 
modified from the coelomic epithelium. 

It is supposed that, because these chlorogogen cells lie in the typhlo- 
sole close to the dorsal blood vessel, they may aid in some digestive 
process. Then, because chlorogogen granules are present in the coelomic 

The Earthworm 269 

fluid of adult worms and make their way to the outer part of the body 
through the dorsal pores, it has been suggested likewise that they may 
have some excretory function. 

Three pairs of calciferous glands ( ), one pair 

in each of the somites from ten to twelve, are found at the sides of the 
oesophagus. The first pair are pouches, pushed out from the alimentary 
canal, which open directly into the oesophagus. The other two pairs are 
swellings of the oesophageal wall. They have a number of small cavities 
which open directly through the epithelium into the oesophagus in 
somite fifteen. 

One writer thinks these glands manufacture carbonate of lime which 
is then secreted in the alimentary tract to neutralize the acid foods, 
while another suggests that the primary function of the glands is merely 
to excrete calcareous matter derived from leaves on which the animal 
feeds. This opinion he bases on the fact that such matter accumulates 
in leaf-tissue and remains in the leaf when it falls. The worms, which 
take in large quantities of calcareous matter but have no shell or bone, 
have no use for it, and so "some special excretory apparatus seems 
necessary." This latter opinion does not oppose the one given imme- 
diately preceding it. But the gizzard and intestinal content of worms 
is, as a rule, acid, so this would seem to oppose both of the above ideas. 
However, this acidification may be the result of fermentations which 
occur in the later stages of digestion. 

It will thus be seen, that many things must be considered before 
one can speak on subjects such as these with any degree of authority 
and positiveness. 

As stated, the earthworm feeds on decaying leaves and animal mat- 
ter. This food is sucked into the buccal cavity. 

Here it receives a secretion from the pharyngeal glands, after which 
it passes through the oesophagus to the crop to be stored temporarily. 
Secretions from the calciferous glands in the oesophageal walls neutralize 
the acids. The gizzard is a grinding organ in which the food is broken 
up into minute fragments by being squeezed and rolled about. Then, 
too, solid particles, such as rough pebbles, which are frequently swal- 
lowed, may aid in the grinding process. The food then passes to the 
intestine, where most of the digestion and absorption take place. 

Digestion in the earthworm is very similar to that of higher animals. 
The digestive fluids act upon proteins, carbohydrates, and fats. Special 
compounds called ferments or enzymes are in the digestive fluids which 
break up complex molecules without themselves becoming permanently 
changed chemically. The three most important enzymes are (1) trypsin 
( ), which dissolves protein; (2) diastase ( ), 

which breaks up molecules of carbohydrates, and (3) steapsin ( ), 

which acts upon fats. These three enzymes are probably in the digestive 

270 General Biology 

fluids of the earthworm. The proteins are changed into peptones, the 
carbohydrates into a sugar compound, and the fats are divided into 
glycerin and fatty acids. 

After this process has taken place, the food is ready for absorption. 
This takes place through the wall of the intestine by osmosis, assisted 
by an amoeboid activity of some of the epithelial cells. 

It will be remembered from our study of the frog that all parts of 
a living- organism must be nourished. The food absorbed is now taken 
into the circulation and made an actual part of the blood. As there are 
no blood vessels in some parts of the earthworm, some of the absorbed 
food is also taken into the coelomic fluid so as to bathe the bloodless 


The blood of the earthworm, unlike that of man, is actually red, 
while the corpuscles are colorless. In man the blood-liquid is colorless, 
and the corpuscles floating about in the blood-plasma are red. This 
means that the pigment haemoglobin ( ) is within 

the corpuscle in man and the higher animals, while it is in solution in 

The following table mentions most of the important longitudinal 
blood-vessels (Fig. 167) : 

(1) The dorsal or supra-intestinal, running along the dorsal surface 
of the alimentary canal, from the posterior end of the body to the 
pharynx. It then divides into many small branches. 

(2) The ventral or sub-intestinal trunk, lying just beneath the 
alimentary canal. It also extends from the posterior end of the body 
to the pharynx where it divides into many small branches. 

(3) The sub-neural trunk, as its name implies, passes along under 
the ventral nerve cord the entire length of the body. 

(4) A pair of lateral-neural trunks (smaller than those above) 
lying, one on each side of the ventral nerve cord. 

As in the frog and all other vertebrates, paired arteries, veins, and 
nerves, pass toward and away from the spinal cord between the various 
vertebrae, so in each segment of the earthworm tiny branches of the 
dorsal and ventral trunks, called parietal ( ) branches, 

pass along the various septa dividing the somites, and connect with the 
body wall, where they split into fine branching capillaries supplying 
and draining the dermal musculature and epithelium. 

Capillaries from the dorsal branch also supply the digestive tract, 
while in the anterior region two lateral vessels supply the reproductive 

It will be remembered that in the study of the frog, the circulatory 
system began with a three-chambered heart. In the earthworm there 
is no separate and distinct organ such as the heart. In its place there 

The Earthworm 


are five pairs of enlarged vessels 
called aortic arches, aortic loops, or 
"hearts," running from the dorsal 
trunk to the ventral through the 
seventh, eighth, ninth, tenth and 
eleventh somites. 

These "hearts," as well as the 
dorsal trunk, furnish the muscular 
contraction and elongation of circu- 
lar and longitudinal muscles which 
force the blood through the vessels. 
Such rhythmic contraction and ex- 
pansion in either blood vessels or 
intestines is known as peristalsis 

( )• 

In the frog there is a systemic 
and pulmonary circulation. The 

earthworm, possessing no lungs, can 
have no pulmonary circulation. 

The blood of the earthworm is 
continuous in closed blood-vessels, 
so it is called a closed systemic cir- 

But, just as there is the closed 
circulation consisting of heart, 
arteries, veins and capillaries in the 
frog, as well as a lymphatic, open 
circulation, by which the lymph passing out of the blood-vessels is able 
to bathe every part of the body, so we speak of a coelomic circulation 
in the earthworm, which is equivalent to the lymph-like substance out- 
side of the blood-vessels, but within the coelomic cavity of the frog. 

The blood is collected from the intestine by two pairs of vessels 
which enter a longitudinal typhlosolar tube. This tube is in turn con- 
nected with the dorsal trunk by three or four short tubes in each somite. 

As there are no circular muscles in the walls of the ventral trunk, 
this cannot contract, so the propelling of blood is caused by the dorsal 
trunk and "hearts" as already stated. This contractile ability of the 
dorsal trunk and "hearts," together with the fact that there are valves 
in both of these vessels which permit blood to flow forward but not 
backward, determines the direction of flow. The valves are just behind 
the openings of the parietal vessels and in front of the openings of the 
hearts. There are other valves also, in some of the other vessels, but 
those just mentioned are the more important in showing how and why 
the blood flows as it does. 

The blood must, therefore, flow forward toward the anterior end of 

A series of diagrams to illustrate the ar- 
rangement of the blood-vessels and the course 
of the circulation in Lumbricus herculeus. 
A. Longitudinal view of the vessels in somites 
8, 9 and 10. B. The blood-vessels as seen in 
transverse section in the same region. C. 
Longitudinal view of the vessels in the intesti- 
nal region. D. Transverse section through the 
intestinal region. sp, supra-intestinal; sb, 
sub-intestinal, and sn, sub-neural longitudinal 
trunks; nl, lateral neural vessels; ht, ht, con- 
tractile vessels or "hearts;" it, intestino-tegu- 
mentary vessels; cv, commissural vessels; af.i, 
afferent intestinal vessels; ef.i, efferent intesti- 
nal vessels; ty, typhlosolar vessel; i, intestine; 
oe, oesophagus; j-.j. septa. (After Bourne 
from a drawing by Dr. W. B. Benham.) 

272 General Biology 

the animal in the dorsal trunk. It is thus forced through the "hearts" 
and, as it reaches the ventral trunk, is sent both in an anterior and a 
posterior direction. From the ventral trunk the blood passes to the body 
wall and nephridia. The lateral neural trunks then receive the blood 
which has gone to the body-wall, while that having gone to the nephridia 
has been expelled. The blood in the sub-neural trunk flows posteriorly, 
then upward through the parietal vessels into the dorsal trunk. The 
anterior portion of the body receives its nourishment from both dorsal 
and ventral trunks. 

The Coelomic circulation consists of the fluid in the coelomic cavi- 
ties. These cavities are continuous throughout all the somites by means 
of dorsal apertures or slits occurring between the various septa and the 
digestive tract. The fluid itself is made up of a colorless plasma with 
white blood cells or leucocytes ( ). This fluid is 

washed back and forth by the movements of the worm and thus bathes 
the endothelial lining of the coelom. 

The amoeboid corpuscles in the coelomic fluid have a remarkable 
power of attacking bacteria and other microscopic organisms such as 
gregarines and infusorians or even small nematode worms. If such 
parasites enter the coelom, the amoeboid cells surround and destroy 
them. Their operations are, however, not confined to the inside of the 
earthworm. The slime of the body surface is in part composed of mucus 
secreted by the skin, and in part of coelomic fluid and its corpuscles 
which find exit through the dorsal pores. The corpuscles are thus able 
to attack and destroy bacteria before they effect an entry into the body. 
There is no doubt that a worm is constantly exposed to these minute 
organisms for the upper layers of the soil teem with them. The slime 
itself is a protection, for it both arrests the bacteria and holds them 
stranded in the trail which- the worm leaves behind it in its progress. 
The application of a grain of some irritant, such as corrosive sublimate, 
enables one to see how a worm protects itself. As soon as the irritant 
touches the skin, the segments in front and behind the seat of injury 
are forcibly constricted, while the affected segment itself swells up in 
consequence of the increased pressure brought to bear upon it from both 
sides. At the same time there is a conspicuous gush of coelomic fluid 
from the dorsal pores in that region and an abundant secretion of mucus 
from the skin itself. Thus the threatened region is, as it were, isolated 
by ligatures from the rest of the body and all the defensive resources 
at once brought to bear upon the enemy. The coelomic fluid is alkaline 
and contains crystals of calcium carbonate and micro-organisms which, 
when isolated and reared in artificial cultures, emit the characteristic 
smell of earthworms. It is, therefore, not improbable that this odor 
is due to the micro-organisms and not really a feature of the worm 

From what has been said above, it will be seen that there is in 
reality no true circulation in the earthworm. 

The Earthworm 273 


The earthworm needs oxygen just as do all animals; but, as it has 
no lungs, it obtains its oxygen through its moist outer membrane. 
Immediately beneath the cuticle there are many capillaries which pre- 
sent a great expanse of blood area somewhat similar to the many capil- 
laries in the lungs of higher forms. The oxygen here combines with 
haemoglobin. The blood gets to these capillaries through the vessels 
supplying the body wall and is then returned to the dorsal trunk by way 
of the sub-neural trunk and the intestinal connectives. 

As the nervous system must coordinate every movement of the 
body, it requires an excellent blood-supply, which is furnished the better 
in the earthworm by the sub-neural trunk lying very close to the ventral 
nerve cord. The nervous system is thus continually supplied with fresh 


Most of the excretory matter is carried outside the body by a num- 
ber of coiled tubes called nephridia, a pair of which lie in each somite 
except the first three and the last. The dorsal pores also serve as ex- 
cretory organs to a minor extent. 

A clear understanding of the nephridia is important, because such 
an understanding will serve in good stead in the study of the excretory 
organs of vertebrates. This is the better understood when it is known 
that the excretory organs of all higher forms develop from embryological 
beginnings quite similar to those of the earthworm. 

Each nephridium (Fig. 168) consists of: 

(1) The funnel or nephrostome ( ), 

(2) The ciliated neck, 

(3) The coiled narrow tube, 

(4) The wide glandular tube, 

(5) The ejaculatory duct opening to the outside. 

The ciliated neck of each nephrostome passes through the anterior 
wall of the somite, close to the mid-ventral line. Each nephrostome, 
therefore, lies in the somite directly anterior to the one containing its 
own nephridium, so that waste matters from any one somite are expelled 
to the outside by the nephridium of the next posterior somite. The 
nephrostomes, or mouths, of the nephridia are flattened fan-like struc- 
tures, consisting of two flattened lamellae or plates, with a narrow slit- 
like opening between them. The large cells, which line the opening, are 
covered with powerful cilia which maintain a constant current toward 
the tubular part of the nephridium. These tubes are developed in coils 
which lie in the posterior parts of the somites. There are three coils 
or turns in each. The third ends in an enlarged portion opening to the 


General Biology 

outside on the ventral wall of the somite. All of the turns are well 
supplied with blood vessels. 

An excellent way of demonstrating the action of these nephridic 
organs is that of injecting carmine powder into the coelom. It will then 
be observed that this foreign substance is taken up by the chlorogogen 
cells, which then break down, freeing the carmine together with frag- 

Wall of Digestive Tract. 
Ciliated Nephrostome. 


Duct of Nephridium. 

Connective Tissue 

Containing Blood Vessels. 
Glandular or Secreting Portion. 
Body-Wall Composed of 
Longitudinal and Circular 
Muscle Fibers and 
Epithelial Layer. 
External Opening. 

Fig. 168. Nephridium. 

ments of the chlorogogen cells, and all are caught up by the current 
made by the nephrostome, and carried through the nephridium to the 
outside. From this experiment the conclusion has been drawn that 
some, at least, of the waste matters of the tissues are brought to the 
chlorogogen cells by the circulation and are acted upon by the fluids of 
those cells. The products of this activity are liberated into the coelom 
by the fragmentation of the cells, and then excreted from the worm by 
the nephridia. 


Notwithstanding the nerve cells scattered about in Hydra, it is 
in the earthworm that we meet with our first organized nervous system 
(Fig. 169). That is, of course, excluding our study of the frog. It will 
be remembered that the nerve cord was on the dorsal side of the frog. 
In the earthworm, and all animals lower than vertebrates, it lies on the 
ventral surface. The knowledge of this fact is quite important and will 
be of use in the later study of evolutionary theories. 

Nerves are sensory, motor, or mixed as we saw in the study of the 
frog. Both sensory and motor nerves run to the muscles of the earth- 
worm, causing reflex action. A reflex action means that an impulse sent 
toward the central nervous system through a sensory nerve, meets a 
motor nerve (the meeting place being called a ganglion), and the motor 
impulse is then returned to the place from whence the sensory impulse 
originated, permitting an organ to move. If such ganglion lies in the 
lower nerve centers, that is, if it lies caudad to the brain, so that an 
impulse from a sensory fiber need not first pass to the brain before 
meeting the motor fiber, it is called a reflex. 

The Earthworm 


Fig. 169. Diagram of the Anterior End of Lum- 

bricus Herculeus to show the Arrangement 

of the Nervous System. 

I, II, III, IV. The first, second, third, and 
fourth segments. 

1. The prostomium. 2. The cerebral ganglia. 
3. The circumoral commissure. 4. The first ven- 
tral ganglion. 5. The mouth. 6. The pharynx. 
7. The dorsal and ventral pair of chaetae. 8. The 
tactile nerves to the prostomium. 9. The anterior, 
middle and posterior dorsal nerves. 10. The an- 
terior, middle and posterior ventral nerves. 
(After Hesse.) 

The ventral nerve cord is in reality a series of ganglia, one pair lying 
in each somite posterior to the fourth. Each pair is connected by a 
nerve cord to the one preceding and following it. In somite four this 
nerve cord divides into two parts, one passing on each side of the 

alimentary tract to again unite 
above the pharynx in the third 
somite. This dorsal union is 
the brain, while the two por- 
tions forming it are known as 
the circum-pharyngeal con- 
nectives. The segmental 
ganglia forming the nerve cord 
are called the sub-pharyngeal 
ganglia. The brain and ventral 
cord form the central nervous 
system. The nerves passing 
from the central nervous sys- 
tem to the various parts of the 
body, constitute the peripheral 
nervous, system. 

The supra - pharyngeal 
ganglia supply the prostomium 
with two large nerves which give off many branches ; they also send 
nerves into somites two and three. One nerve extends out from each 
circum-pharyngeal connective. In each somite, from the fourth to the 
posterior end of the body, three pairs of nerves arise, two pairs from 
the ganglionic mass and one pair from the sides of the nerve cord just 
behind the septum which separates the somite from the one preceding. 

Each enlargement of the ventral nerve cord really consists of two 
ganglia, which are closely fused together. In transverse section these 
fused ganglia are seen to be surrounded by an outer thin layer' of 
epithelium, the peritoneum, and an inner muscular sheath containing 
blood vessels and connective tissue as well as muscle fibers. Near the 
dorsal surface are three large areas, each surrounded by a thick double 
sheath and containing a bundle of nerve fibers. These are called neuro- 
chords or "giant fibers." Large pear-shaped nerve cells are visible near 
the periphery in the lateral and ventral parts of the ganglion. 

The nerves of the peripheral nervous system are either efferent or 
afferent. Efferent nerve fibers are extensions from cells in the ganglia 
of the central nervous system. They pass out to the muscles or other 
organs, and, since impulses sent along them give rise to movements, 
the cells of which they are a part, are said to be motor nerve cells. The 
afferent fibers originate from nerve cells in the epidermis which are 
sensory in function, and extend into the vertral nerve cord. 

276 General Biology 


The sensitiveness of lumbricus to light and other stimuli is due to 
the presence of a great number of epidermal sense organs. These are 
groups of sense cells connected with the central nervous system by 
means of nerve fibers, and communicating with the outside world 
through sense hairs which penetrate the cuticle. More of these sense 
organs occur at the anterior and posterior ends than in any other region 
of the body. The epidermis of the earthworm is also supplied with 
efferent nerve fibers which penetrate between the epidermal cells forming 
a sub-epidermal network. 


The earthworm, like Hydra, is hermaphroditic (Fig. 170) 
( ), that is, has both sexes in each animal. < 

The female reproductive organs, the ovaries, lie in somite thirteen, 
the oviducts in somites thirteen and fourteen, while two pairs of seminal 
receptacles or spermathecae lie in somites nine and ten. 

The ovaries, which are small pear-shaped bodies lying on either side 
of the mid-ventral line, are attached by their larger ends to the ventral 
part of the anterior septum. 

The oviducts are made up of various parts. The ciliated funnel lies 
just posterior to each ovary and passes through the septum, dividing 
somites thirteen and fourteen, where it has an enlargement known as 
the egg sac. It then narrows into a thin duct which opens to the external 
part of the body on the ventral surface near the center of somite fourteen. 

The spermathecae or seminal receptacles are white spherical sacs 
near the ventral body-wall, one pair each in somites nine and ten. These 
open to the outside through the spermathecal pores lying between 
somites nine and ten, and ten and eleven. 

The male reproductive organs consist of two pairs of glove-shaped 
testes, one pair each in somites ten and eleven. Their positions in the 
somites are similar to the ovaries. The vas deferens ( ), 

the male organ homologous to the female oviduct, is likewise a ciliated 
funnel serving as the mouth of the duct through which the sperm pass. 
This lies immediately behind each testis. The duct itself passes through 
the septum just back of the funnel, where it forms several convolutions, 
and then extends backward near the ventral surface. The two sperm 
ducts which arise on either side of the midventral line, unite in somite 
twelve and then run back as a single tube, opening to the outside through 
the spermiducal pore on somite fifteen. In a sexually mature earth- 
worm, the testes and funnel-shaped inner openings of the sperm ducts 
are inclosed by large white sacs, the seminal vesicles, which lie in somites 
nine to twelve. There are three pairs of these sperm sacs, one in somite 
nine, one in somite eleven, and the third in somite twelve. In somites 
ten and eleven there are central reservoirs, 

The Earthworm 


The testes are rather difficult 
to find in a mature worm because 
they are quite small and the dor- 
sal wall of the vesicle must first 
be removed. 

The sperm are developed in 
the testes and stored in the sem- 
inal vesicles from which they are, 
during the period of copulation, 
injected into the seminal recep- 
tacles of another worm. Fertili- 
zation actually takes place outside 
the body. 

When the earthworm is sex* 
ually mature, a clitellum, or 
cingulum, is formed, covering 
some six or seven segments. This 
is a thickened portion often sup- 
posed to be a scar formed by the 
worm after having been injured 
or cut in two. Mating may take 
place at any season of the year, 
but occurs more frequently in 
warm damp weather. 

Again quoting Latter : Two 
worms from adjacent burrows, "each retaining a firm hold in its own 
burrow by means of the flattened tail, apply their ventral surfaces to 
one another so as to overlap for about a third of the length of the body. 
The head of each worm points toward the tail of the other. The clitel- 
lum of each secretes a band of mucus which binds the two worms firmly 
together, so firmly, indeed, as to cause two well-marked constrictions, 
while a slimy covering, the slime tube, surrounds the two worms from 
the 8th to the 33rd segments. The seminal fluid, containing spermatozoa 
( ) and spermatophores ( ), 

flows within the slime-tube; during sexual union, in the early stages 
of the formation of the cocoons, spermatophores cover the dorsal and 
lateral surfaces of segments 9, 10, and 11 of each worm and are packed 
between the two worms. The spermatozoa flow backwards from the 
male aperature in a longitudinal groove on each side to the receptacula 
(spermathecae) of the other worm, the grooves of the two animals 
together forming a temporary tube. Hence only one worm can emit 
spermatozoa at any given time, otherwise there would be opposing 
currents. The worms are so placed that the ninth segment of each is 

Lumbricus Herculeus. 

A. A view of the organs contained in the 
first twenty-two somites, as seen when the animal 
is opened by a longitudinal dorsal incision, and 
the body walls are pinned out without cutting the 
septa. The pins are placed in the 3rd, 9th, and 
18th somites. B. View of the first sixteen somites 
of the same worm after removal of the alimen- 
tary tract, to show the nervous system and re- 
productive organs. be, buccal cavity, cut across; 
eg, cerebral ganglia; g, gizzard; int, intestine; 
nph, nephridia; od, oviduct; oe, oesophagus; ov, 
ovary in somite 13; ph, pharynx with radiating 
muscular strands; prv, proventriculus ; s, septa; 
sd, sperm duct; sf, seminal funnels; spth, sper- 
mathecae in somites 9 and 10; sp.s, sperm sacs; 
t, testis. (After Bourne.) 

278 General Biology 

opposite the 32nd (first clitellar) of its mate, then the thickened clitellum 
forms a barrier past which no flow of seminal fluid can take place. 

"The long genital setae in the 'tubercula pubertatis' ( ) 

of the clitellum, and of segments 10 to 15, are probably used, the former 
to liberate the cocoon from its seat of origin, and the latter series to 
hold the cocoon off the ventral surface in the region of the oviducal 
openings and those of the spermathecae, and thus allow ova and sper- 
matophores to pass into the cocoon as it passes forward. These special- 
ized setae replace those of ordinary form as the worm reaches maturity. 
The eggs do not pass out of the oviduct till near the end of the act of 
mating. Each of the two worms forms a cocoon, and slips out of the 
cocoon backward, passing the cocoon forward over its head. The cocoon 
being elastic closes its two open ends as soon as the body of the worm 
is withdrawn, and becomes more or less lemon-shaped, its bulging center 
being occupied by about four eggs, spermatozoa and albuminous material 
produced by the so-called capsulogenous glands, which may be seen on 
the ventral side of some of the segments in front of the clitellum. The 
cocoons, at first white but soon becoming yellow, are left in the earth, 
and as a rule only one of the contained eggs produces a young worm. 
The size of the cocoons differs in the various species, those of L. 
terrestris are from 6 to 8 mm. long by 4 to 6 mm. broad, of Eisenia. 
foetida from 4 to 6 mm. long by 2 to 3 mm. broad. There is some doubt 
as to the precise function of the spermathecae. It seems certain that 
the spermatozoa contained in them, are derived from some other worm. 
It is also the case that these organs are full of spermatozoa prior to 
sexual union, and are empty subsequent to that act, at any rate when 
cocoons are formed and eggs deposited. Worms have been observed to 
separate without producing cocoons, and though perhaps in some in- 
stances the separation may have been due to disturbance caused by 
observation, yet there is reason to think that two unions are necessary, 
one to fill the spermathecae, and a second to form cocoons. In such a 
case it is probable that each worm acts as a carrier oi spermatozoa from 
its first to its second mate, i. e., worm A gets its spremathecae filled by 
the spermatozoa of B in the first union, and passes these spermatozoa 
to C in the second. The actions are probably often reciprocal. Accord- 
ing to Goehlich, while spermatozoa are flowing from one worm to the 
spermathecae of the other, there is given out from the spermathecae 
of the former a small quantity of mucus which hardens when it reaches 
the air. A second portion of mucus, containing a group of spermatozoa, 
is then emitted. This becomes attached to the first mass, and with it 
forms a spermatophore. The whole spermatophore is attached to the 
body of the other worm close to the clitellum. When the cocoon is 
made, the spermatophores are rubbed off into it as the animal withdraws 

"Light could probably be thrown on this matter by some such 

The Earthworm 279 

experiments as follow: Keep a number of worms, each in a separate 
flower-pot, from infancy to maturity ; kill a few and examine the con- 
tents of their spermathecae (it is conceivable that a worm may be able 
to pass spermatozoa into its own spermathecae) ; allow the remainder 
to mate once, and note if cocoons are deposited ; kill some and examine 
the contents of spermathecae; allow the rest to mate a second time, 
pairing some with their former mates and others with different mates. 
Kill all and examine spermathecae." 

In plants and animals, where both sperm and eggs are found in the 
same individual, there is usually a different period for the maturing of 
each, or some apparatus like this of the earthworm is brought into play 
so that it is very seldom that the same organism can fertilize itself. 

The sperm-mother cells are derived from the testes and deposited in 
the seminal vesicles. They are not fully developed, or as we say, 
"mature," however, when they leave the testes, and so must continue 
their development in the seminal vesicles. 

The sperm-mother cells, or primordial germ-cells, from which the 
sperm are developed in the testes, have their nuclei divide into 2, 4, 8, 
or 16 daughter nuclei which become arranged in a single layer near the 
periphery of the protoplasm which has not divided. Cell walls then 
appear, extending inward into the undivided protoplasmic mass. These 
newly-formed cells now divide again, forming as high as from 32 to 128 
cells, when the whole mass breaks up into smaller colonies. These 
nucleated cells, which are to become sperm, are called spermatogonia. 
These spermatogonial colonies become spherical, each containing 32 pri- 
mary spermatocytes, all of which are still fastened by cytoplasmic 
threads to the central protoplasm. This whole 32 celled colony is now 
called a blastophore. 

Each colony of primary spermatocytes causes the formation of 64 
secondary spermatocytes, and these divide into 128 spermatids. The 
latter then metamorphose ( ) into spermatozoa. 

The number of chromosomes in the spermatozoa is sixteen. This is one- 
half the number contained in the somatic cells, a reduction having taken 
place during maturation by the union of the chromosomes two by two in 
the secondary spermatocytes, and a subsequent separation when the 
spermatids were formed. 

The head of the spermatozoon is practically all nuclear material. 
The mid-piece is what was formerly the centrosome, while the cytoplasm 
formed the tail. But as it is only the head which actually enters and 
fertilizes the Ggg, the tail being used only for locomotive purposes, it 
will be seen why nuclear material is considered so very important. 


The egg-mother cells are found in the ovary in various stages of 
growth, beginning at the basal end of each ovary where the most primi- 


General Biology 

Segmentation and early stages of development of 
Lumbricus. A, B, C, D, successive stages of 
segmentation. E. Blastula stage. F. Com- 

mencement of invagination; the macromeres 
form a flat plate on the ventral side. G. An embryo 
somewhat younger than F. viewed from above, show- 
ing the mesomeres and mesoblast rows derived from 
them. H. Gastrula stage viewed from below, show- 
ing the wide oval blastopore bounded by macromeres; 
at the sides the micromeres are growing over the 
macromeres. /. Later stage, showing the elongated 
blastopore and the further overgrowth of the macro- 
meres by the micromeres. K. Optical longitudinal 
section through a later stage after the closure of the 
blastopore. bp, blastopore; ec, ectoderm; en, endo- 
derm; ent, enteron; mac, macromeres; mes, meso- 
blast; mic, micromeres; mm, mesomeres. (From 
Bourne after Wilson.) 

tive germ-cells are found. The 
ova increase in size toward the 
extreme end, where the germ- 
cells are distinctly rec- 
ognizable as eggs. Each 
egg is surrounded by a follicle 
( ) of 

nutritive cells. The eggs sep- 
arate from the end of the ovary 
and dropping into the body- 
cavity, pass into the ciliated 
end of the oviduct which leads 
to the egg-sac where part of 
the maturation takes place. 
From here they either pass out 
into the cavity of the slime- 
tube and are conveyed from the 
external openings of the ovi- 
duct in somite 14 to the cocoon, 
or they enter the cocoon itself 
when it passes over this 
somite during deposition. The 
eggs are actually fertilized by 
the spermatozoa after the 
cocoon is shed and before the 
egg has completed its matura- 

tion process. 

The egg of the earthworm is holoblastic (Fig. 171) although cleav- 
age is unequal, the first division resulting in one large and one small cell. 
The second cleavage divides the small cell into two equal parts, but 
cuts off only a small portion from the larger one. The small cells are 
called micromeres, and the large ones macromeres. Cleavage is very 
irregular after this second division. The micromeres are the animal cells, 
and the macromeres the vegetative cells. 

A cavity, the blastocoele, soon forms between micromeres and 
macromeres, resulting in a blastula. 

Two of the larger cells of the blastula project down into the 
blastocoele. These continue dividing and form two rows of small cells 
from which the mesoderm is to form. They are, therefore, called 
mesomeres, while the two rows formed from them are known as meso- 
blastic bands. During the time these bands are forming, the blastula 
becomes flattened, the larger cells form a plate of clear columnar cells, 
and the small cells spread out into a thin dome-shaped epithelium. 

The mesomeres lie toward the posterior end of the blastula, and the 

The Earthworm 


mesoblastic bands lie along the longitudinal axis of the worm, showing 
the beginnings of bilateral symmetry. 

A gastrula is now formed by the invagination of the plate of large 
cells, this invagination continuing until only a slit remains. This tiny 
opening or slit is called the blastopore, while the cavity is the enteron. 

Fig. 172. Polygordius Appendiculatus. 

A, dorsal view. an, anus; ct, cephalic 
tentacles; h, head. B, trochosphere larva, an, 
anus; e, eye-spot; m, mouth. C and D, stages 
in development of trochosphere into the worm. 
pnp, pronephridium. (From Bourne, after 

Fig. 173. Nereis Pelagica, L. (After Oersted.) 

There are now three germ-layers. The mid-layer or mesoderm 
already began forming before gastrulation. 

The large clear cells which invaginated have become the inner lining 
of the enteron and form the entoderm; the outer portion is ectoderm, 
while the mesoderm is made up of the two mesoblastic bands which lie 
between ectoderm and entoderm. 

As the earthworm is to be our example of the coelomates, it is of 
value here to observe how the coelom is formed. 

The mesoderm separates into the two layers on each side of the 
body. A cavity forms between these layers. This cavity is the coelom. 
The outer portion of the divided mesoderm is called the somatopleure 
( ), the inner layer the splanchnopleure ( ). 

The muscles of the body-wall are formed from the somatopleure, 
while the splanchnopleure forms the muscles of the alimentary canal. 
After the germ-layers are formed, the embryo elongates, the anterior- 
posterior axis passing through the blastopore. There are various in- 
pushings from the ectoderm which become the elements of the nervous 
system. Such beginning cells are called neuroblasts if they form nerves. 

There are also separations from the mesoderm forming nephroblasts 
if they form nephridia, somatoblasts if they form muscles, etc. 

The ectoderm turns in at both anterior and posterior ends, the for- 

282 General Biology 

mer forming the mouth or stomodeum ( ), the latter 

the anal opening or proctodeum ( ). 

The chlorogogen cells are formed from mesoderm, as are also the 
blood-vessels, muscles, reproductive organs and seta sacs. The young 
worm is now ready for an independent life and leaves the cocoon after 
from two to three weeks. 

The following table will give a summary of the important tissues 
derived from the various germ-layers : 


Oesophagus, Outer Epithelium, Muscles, 

Crop, Nervous System, Coelomic Endothelium, 

Gizzard. Stomodeum, Chlorogogen Cells, 

Proctodeum, Calciferous Glands, 

Ends of Nephridia. Blood vessels, 


Nephridia, functional parts, 
Seta Sacs, 
Reproductive Organs. 


As shown by their home-life, worms are apparently fond of having 
their bodies in contact with solid objects. Moisture causes a positive 
reaction if such moisture comes in direct contact with the worm's body. 
This is well illustrated by placing the earthworm, Allobophora foetida 
(the small manure worm), on a piece of dry filter paper when it will 
not react, but as soon as moisture is applied it begins to burrow, pro- 
vided this moisture or liquid is taken from manure. 

Darwin supposed that the earthworm's ability to distinguish edible 
from inedible food lay in the sense of contact. This would make contact 
in the earthworm act as a sort of taste organ. Various chemicals which 
cause a reaction, may be due to this sort of secondary taste-ability. 

While there are no eyes, light causes the animal to react. This is 
shown by its moving away from lighted areas. The manure worm, how- 
ever, will respond positively to a very faint light. The preferable colors, 
when very faint, are red, green and blue in the order given, though it 
does not follow from this that the earthworm can distinguish colors. 
Its ability consists, in all probability, of ''feeling" different rays of light 
as well as different intensities. 

It has also been noted that, if a previous stimulus is much stronger 
than a succeeding one, the first will naturally continue to react and 
cause either no reaction to a second or at least lessen such reaction. 
An example of this is found when the animal is feeding or mating. Light 
which under normal conditions causes a negative reaction, may have 
no effect whatever under such circumstances, the instinctive reaction 
of the primary instinct being stronger than the artificial secondary 

The Earthworm 




Any part of an earthworm may be cut off at any point between the 
end of the prostomium and the fifteenth to the eighteenth segment and 
a new anterior end will grow out from the cut end of the body. This 
will consist of a single segment if only one segment was removed ; two 
segments, if two segments were removed ; and of three, four, or five seg- 
ments, if three, four, or five seg- 
ments were removed. But never 
more than segments one to five are 
regenerated, regardless of the num- 
ber removed, and no new reproduc- 
tive organs appear if the original 
ones were contained in the severed 
piece. If the cut is made behind 
segment eighteen, a tail will grow 
out from the cut surface of the pos- 
terior piece, thus producing a worm 
consisting of two tails joined at the 
center. Such a creature cannot take 
in food, and must slowly starve to 
death. When the regenerated part 
is different from the part removed, 
as in the case just cited, the term 
heteromorphosis is given to the phe- 

Regeneration of a tail differs 
from that of a head, since more than 
five segments can be replaced. The 
anal segment develops first, and then 
a number of new segments are intro- 
duced between it and the old tissue. 
The rate of regenerative grow T th 
depends upon the amount of old 
tissue removed. If only a few seg- 
ments of the posterior end are cut off, a new tail regenerates very 
slowly; if more are removed, the new tissue is added more rapidly. In 
fact, the rate Of growth increases up to a certain point as the amount 
removed increases. The factors regulating the rate of regeneratior; have 
not been fully determined, although several possible explanations have 
been suggested. 

Pieces of earthworms may be grafted upon other worms without 
much difficulty. Three pieces may be so united as to produce a very 

Fig. 174. 

A. Hirudo medicinalis, about life size. 

1. Mouth. 2. Posterior sucker. 3. Sen- 
sory papillae on the anterior annulus of each 
segment. The remaining four annuli which 
make up each true segment are indicated by 
the markings on the dorsal surface. 

B. View of the internal organs of Hirudo 
medicinalis. On the left side the alimentary 
canal is shown, but the right half of this 
organ has been removed to show the excretory 
and reproductive organs. 

1. Head with eye spots. 2. Muscular 
pharynx. 3. 1st diverticulum of the crop. 4. 
11th diverticulum of the crop. 5. Stomach. 
6. Rectum. 7. Anus. 8. Cerebral ganglia. 9. 
Ventral nerve cord. 10. Nephridium. 11. 
Lateral blood-vessel. 12. Testis. 13. Vas de- 
ferens. 14. Prostate gland. IS. Penis. 16. 
Ovary. 17. Uterus — a dilatation formed by 
the conjoined oviducts. (After Shipley and 

284 General Biology 

long worm; the tail of one animal may be grafted upon the side of 
another, producing a double-tailed worm ; or the anterior end of one 
individual may be united with that of another. In all such experiments 
the parts must be held together by threads until they become united. 

The Annelida are divided into three classes, as follows: 

(1) Class Archiannelida (Gr. arche, beginning — Lat. annellus, 
ring). The Polygordius (Fig. 172) is the typical example. This class 
is without setae or parapodia. 

(2) Class Chaetopoda (Gr. chaite, bristle — pous, foot). Nereis, 
the common sand-worm, and the earthworm are classic examples. 
Nereis differs from the earthworm in having a pair of chitinous jaws, 
a pair of tentacles, and two pairs of eyes on the prostomium, as well as 
in having a pair of palpi, and four pairs of tentacles on the peristome. 
The parapodia are used for locomotion, while the lobes of the parapodia 
are well supplied with blood-vessels and serve as gills. Then, too, there 
are jointed locomotor-setae on each parapodium, while the muscles which 
move the parapodium, are attached to two buried bristles, called aciculae, 
which serve as a sort of internal skeleton. The sense organs of Nereis 
are also developed more highly than those of Lumbricus, the tentacles 
serving as organs of touch, while the palpi are thought to act as organs 
of taste, and the eyes, of sight. 

Nereis (Fig. 173) is the example of the sub-class known as Poly- 
chaeta (on account of its many foot-like structures), while such worm- 
like water-animals as Tubifex, Dero, and Nais, usually serve as the ex- 
ample of the sub-class, Oligochaeta (having few setae). 

(3) Class Hirudinea. (Lat. hirudo, leech.) These are worm-like 
animals living in fresh water and on land. They are commonly called 
leeches. They are flattened dorso-ventrally. The external segmentation 
does not correspond to the internal segmentation. The leeches are dis- 
tinguished from the earthworm by having definitely thirty-three seg- 
ments, two suckers (one at each end), and no setae (except in one 
genus). They are hermaphrodites. 

The most important example is the medicinal leech, known as 
Hirudo medicinalis (Fig. 174), normally about four inches long, though 
capable of much contraction and expansion. Not only are these animals 
used to draw blood from patients, but Lambart advises against drinking 
water which is not filtered, especially in the tropics, as the small leeches 
may be swallowed. When swallowed, they attach themselves below the 
larynx and, instead of releasing themselves when filled with blood as 
they do on an external surface, they seem to draw a small amount of 
blood and then migrate to another spot close by and begin the same 
process, thus causing considerable anaemia (loss of blood). 

This is readily understandable when it is realized that the leech 
has three chitinous jaws to form the mouth (which lies within the an- 
terior sucker). These jaws bite into a region, and a secretion from the 

The Earthworm 285 

mouth-glands is poured out which prevents the host's blood from coagu- 
lating. It is thus difficult to stop the bleeding after the animal has 
moved to a new location. 

The digestive tract of the leech is especially adapted to the diges- 
tion of blood of vertebrates, upon which the leech feeds. There is a 
muscular pharynx and a short oesophagus leading to the crop. This 
crop has eleven branches or diverticulae. Then there is a stomach, an 
intestine, and an anus. The leech can ingest blood to the amount of 
about three times its own weight. 

A peculiar kind of connective tissue, known as botryoidal 
( ) tissue, develops in what should be the coelom. 

This body-cavity is, therefore, very small. There are also spaces in the 
coelom, called sinuses, which are not filled with this tissue. 

There are seventeen pairs of nephridia, quite like those of the earth- 
worm (except that they sometimes do not have an internal opening) 
which carry waste products from the coelomic fluid and from the blood. 
Respiration takes place at the surface of the body through the many 
blood-capillaries found in the skin. 

There are nine pairs of segmentally arranged testes which empty 
their sperm into the vas deferens, then into a much-folded tubule called 
the epididymis. Here they are fastened into bundles known as sper- 
matophores. They are then ready to fertilize the eggs of another leech, 
after passing out of the copulatory organ. 

The eggs develop in a single pair of ovaries, from which they pass 
through the oviducts into the uterus, and finally out through the genital 
pore situated on the ventral side of the ninth segment. A cocoon is 
formed after copulation quite like that in earthworms. 



CONSIDERED systematically the flatworms and round worms 
should be placed before the earthworm as they are not coelomates. 
But, as the average man always thinks of a sort of segmented 
animal similar to an earthworm when worms are mentioned, and medical 
men likewise are not very accurate when they discuss these animals, the 
student is more likely to remember the three types of worms if he thinks 
of them all at once and notes their similarities and differences. 

With the exception of the leech (Hirudo medicinalis) commonly 
used to draw blood, the annelids are of little importance from a medical 
standpoint. However, the flatworms and round unsegmented worms have 
come to have a very considerable bearing on the human being from a 
pathological standpoint. 


The flatworms (which constitute the phylum Platyhelminthes) are 
subdivided into the following three classes : 

Class I. Turbellaria (Lat. turbo, I disturb), with ciliated ectoderm; 
free-living habit, example : Planaria. 

Class II. Trematoda (Gr. trema, a pore; eidos, resemblance), with 
non-ciliated ectoderm; suckers; parasitic habit, example: Fasciola 
hepatica (liver fluke), and 

Class III. Cestoda (Gr. kestos, a girdle; eidos, resemblance)., with 
body of segments ; without mouth or alimentary canal ; parasitic, exam- 
ple : Taenia (tapeworm). 


Turbellaria are the only flatworms which are not parasitic. They 
live on the lower surface of submerged stones and debris close to the 
margin of ponds, springs and lakes. Most of these are Planaria (Fig. 
175), but often a longer worm is found (from ten to fifteen millimeters), 
which is called Dendrocoelum lacteum. 

Planaria crawl about among aquatic plants to seek food. The cilia 
covering the ectoderm assist in this movement, though the animal also 
contracts and expands its body. As soon as Planaria finds a small 
animal suitable for its food, the proboscis, lying near the center of the 
body, is practically turned inside out through the mouth. This proboscis 
grasps the food and draws it into the body. As the mouth is near 
the center of the ventral surface, the proboscis can be extended in any 

Flatworms and Threadworms 


The digestive system consists of the mouth, proboscis or pharynx 
(which lies in a muscular sheath), and three chief interior intestinal 
branches, one running forward to the head end of the body and two 
leading tailward. Many small side pouches, or diverticula, protrude. In 
fact, every part of the body has such a pouch. This means that all 
parts of the body can take nourishment immediately from the digestive 
tract so that Planaria need no circulatory system. All non-digested food 
must be egested through the mouth as there is no anal opening. 

In some forms a definite green substance appears, due to the 
zoochlorellae or symbiotic one-celled plants which live in the middle 

Food is digested both intercellularly and intracellularly, which 
means that a part of the food is digested in the intestine proper by 

secretions poured out from cells 
in the intestinal walls ; and, 
that food may also be digested 
by pseudopodia extending from 
cells in the intestinal walls. In 
the latter case the pseudo- 
podia take in the undigested 
food to the cell which then 
digests it. 
External Appearance. 

Planaria is bilaterally 
symmetrical and dorso-ven- 
trally flattened. The head-end is blunt and the tail-end tapers. It is 
usually less than half an inch in length. The common American species 
is known as Planaria maculata, It has a definite pair of eye-spots. 

Turbellaria are metazoans and triploblastic. The mesoderm con- 
sists mostly of muscles and loose parenchyma cells. The coelom is rep- 
resented by the genital sacs. 

Turbellaria are classified according to the type and number of 
branches found in the digestive tract. 

In some turbellaria, though not in planaria, there are special ecto- 
dermal cells which secrete mucus, or produce rod-like bodies called 
The Excretory System. 

The excretory system (Fig. 176) consists of two irregular, longi- 
tudinal, much-coiled tubes, one on each side of the body. Near the 
anterior end, these two tubes are connected by a transverse vessel. The 
longitudinal vessels open to the exterior by two small pores on the dorsal 
surface of the animal. 

Many fine tubules branch off from these main tubes and ramify 
through all parts of the body, terminating in large flame-cells (Fig. 177). 

Fig. 175. A. Planaria polychroa X about 4. 

1. Eye. 2. Ciliated slit at side of head. 3. Mouth 
of proboscis. 4. Outline of the pharynx sheath into 
which the pharynx can be withdrawn. 5. Reproduc- 
tive pore. 

B. Dendrocoelum graffi. (Woodworth.) 


General Biology 

Each of these flame-cells (which are characteristic of the flatworms) 
consists of a central cavity into which a bundle of cilia project. The 
flickering of the cilia look something like a candle-flame, and it is this 
shape which give them their name. It is the flame-cell which is con- 
sidered the real excretory organ of the ani- 
mal, though some writers think it may also 
have some respiratory functions. 
The Nervous System. 

There are two lobes (Fig. 176) of nerv- 
ous tissue beneath the eye-spots. These are 
usually called the brain. There are also two 
longitudinal nerve-cords, one on each side 

Fig. 176. Anatomy of a Flatworm. 
en, brain; e, eye; g, ovary; i^, i 2 , i 3 , 
branches of intestine; hi, lateral nerve; m, 
mouth; od, oviduct; ph, pharynx; t, testis; 
u, uterus; v, yolk glands; vd, vas deferens; 
d", penis; ?, vagina; tf , 9, common genital 
pore. (From Lankester's Treatise, after v.. 

Flame-cell of Planaria. 

opening into the excretory 
tubule. (From Lankester's Treatise.) 

of the body, connected by transverse nerves. Nerve branches pass into 
the head proper from the brain region, so that the anterior end becomes 
the more sensitive. 
The Muscular System. 

Immediately beneath the ectoderm, a group of muscles form a 
dermo-muscular sac around the internal organs. There are two layers, 
an inner longitudinal, and an outer circular layer. 
The Reproductive System. 

Planaria are hermaphroditic, having both male and female repro- 
ductive organs (Fig. 176). These animals nevertheless often reproduce 
by fission. Each animal has numerous spherical testes which are con- 
nected by small tubules called vasa deferentia. The single vas deferens 
from each side of the body empties into, or through, the cirrus into the 
genital cloaca. 

At the base of the cirrus there are a seminal vesicle and several uni- 
cellular prostate glands. 

After the sperm are formed in the testes, they pass to the seminal 
vesicle through the vasa deferentia, and remain there until needed for 

Flat worms and Threadworms 



Fig. 178. Regeneration of Planaria maculata. 
A, normal worm. B, B 1 , regeneration of 
anterior half. C, C 1 , regeneration of posterior 
half. D, cross-piece of worm. D 1 , D 2 , D 3 , D*, 
regeneration of same. E, old head. E 1 , E 2 , E 3 , 
regeneration of same. F, F 1 , regeneration of 
new head on posterior end of old head. (From 
Hegner after Morgan.) 

The ovaries are two in number. From these the two long oviducts 

(which possess many yolk-glands) connect with the vagina. The vagina 

opens into the genital cloaca. The uterus also connects with the cloaca. 

After the eggs ripen, they pass from the ovary through the oviducts 

(where they collect yolk from the 
yolk-glands) and finally reach the 
uterus. Fertilization occurs in the 
uterus. Cocoons are formed, each 
containing from four to twenty eggs 
and several hundred yolk-cells. 

As already stated, Planaria may 
also reproduce by fission. This 
means in this instance that when 
the hindermost portion of the ani- 
mal is grown, it breaks off from the 
fore part to produce a new animal. 

From the laboratory point of 
view, Planaria is probably the most 
available animal one can find to 
show regeneration experiments. 
This is especially true because the parts to be regenerated grow very 
rapidly, each day marking a definite growth region. 

Almost any part of the animal will re-grow, but there are portions 
quite specialized in what is re-grown. If, for example, the head is cut 
off directly behind the eyes, the more anterior part will regenerate a 
new head but no body, thus making a two-headed animal. Such speciali- 
zation is called polarity. (Fig. 178.) 

Two types of eggs are laid. In the summer the eggs are thin- 
shelled and develop quickly, while in the autumn the "winter eggs" are 
laid. These are thick-shelled and lie dormant until spring before 


All the trematodes are parasitic. Some are monogenetic; that is, 
the adults lay eggs which hatch into forms like their parents, all living 
on the outside of their host. These are said to have a simple life-history. 
This type of animal is usually found on cold-blooded vertebrates, such 
as frogs, fishes, etc. 

The endoparasitic trematodes (those which live in the internal or- 
gans of a host, whether that be in the liver, lungs, intestines, bladder 
or other similar internal structure), are mostly digenetic. This means 
that the parasite must pass through more hosts than one to complete its 
life cycle. 

The liver fluke, Fasciola hepatica (Fig. 179) is the form usually 
studied in the laboratory. 


General Biology 

The adult liver fluke lives in the bile-ducts of the sheep's liver and 
is continually laying eggs which are carried through the intestine of 
the host to the outside in the faeces. If these eggs become moist they 

Fig. 179. 

Stages in the Life-History of the Liver Fluke, 
Distomum Hepaticum. 

1, Egg filled with large vitelline cells in which the segmenting 
ovum, em., is embedded; o., operculum; 2, Miracidium larva with 
large ciliated cells, the eyespot e., and the interior papilla, pa. 
3, Miracidium boring its way into the tissues of Limnaea; f-f., flame 
cells. 4, a sporocyst containing one fully developed and several de- 
veloping rediae (R.); e., the degenerate eyes. 5, a redia containing 
several daughter rediae in various stages of development; m., 
mouth; ph., pharynx; ent., enteron; r., muscle collar; p., posterior 
processes. 6, a cercaria; m., mouth; s'., anterior, and s ff ., poster- 
ior suckers; cs., cystogenous cells. (After Thomas.) 

hatch into tiny ciliated larvae called miracidia. These larvae swim about 
until they find a pond snail. This found, the larvae bore their way 
into the snail where a complete change takes place in the parasite. It 
takes about two weeks for the fluke larvae to form a sac-like sporocyst. 
Each germ-cell in this sporocyst passes through a blastula and gastrula 
stage and then becomes a second kind of larva which is now called a 

Flatworms and Threadworms 


redia. These rediae then break through the sporocyst and enter the 
host's liver. The rediae have germ-cells within them, and these germ- 
cells give rise to little cercaria which look something like tiny tadpoles. 
These tadpole-like cercaria leave the snail and swim to the shore to form 
cysts on surrounding vegetation. 

As the sheep pass along and eat the vegetation bearing these cysts, 


Due to 

Fig. 180. Schistosomum Haematobium. 

(Distoma Haematobium.) 

From the submucosa of the large intestine of man. 

(From a photograph lent the author by 

Dr. E. L. Miloslavich.) 

the life-cycle is again begun. It will be noted from the account just 
given that the larval stages breed in cold-blooded animals, while the 
adult stages must have warm-blooded animals for their hosts. 

The liver fluke is by no means unknown to affect the human liver, 
and where this is known to be the case, great care must be exercised 
in eating uncooked vegetables. 

From the complicated life-cycle the liver fluke displays, it can 
readily be understood that many thousands of eggs must be produced 
by a single animal if liver flukes are not to die out; for, it is not at all 
likely that many of the miracidia wall find a snail host; and then again, 
it is not very likely that many of the cysts on the shore vegetation will 
be eaten by sheep. 

One liver fluke will produce as high as five hundred thousand eggs, 
and a single sheep may contain over two hundred adult flukes. This 
means that over a hundred million of eggs may develop in a single 
Trematode Infections. 

Schistosomum haematobium (Fig. 180), (also called Bilharzia 
haematobia), which causes the disease known as bilharziosis, is by no 


General Biology 

Schistosoma Japonicum. 

<S , male, containing the female 
the gynaecophorous groove, gng. 

?, in 

means uncommon in tropical countries such as Asia and Africa, and is 
sometimes found in Europe and America. 

The mature worm lives in the branches of the portal veins so that 
the eggs are easily distributed (with the blood) into the liver and other 
organs of the body. The eggs, which are the true cause of the disease, 
have a tendency to affect the urinary apparatus, causing a bloody urine 

to be discharged and also causing de- 
structive and over-growth processes in 
the bladder, urethra, and surrounding 
parts. All these infected parts are 
loaded with eggs so that abscesses and 
fistulas form. Similar conditions may 
take place in the rectum. Ten per cent 
of. all patients in Cairo were found to 
be infected, while seven and a half per 
cent of all army recruits in Egypt 
showed the eggs in their urine. 

Schistosomum Japonicum is the 

Japanese species. 

This blood-fluke is peculiar in that it has separate sexes, the male 

being carried about by the female in a gynaecophorous canal (Fig. 181). 

The eggs are oval and a terminal spine is found at one end. The 

eggs hatch in water, so they may be taken in with raw vegetables or 

even with drinking water. 

It is an interesting fact that animal parasites often cause no pain, 
but are on that very account the more dangerous. The patient infected 
pays no attention to his infection, and the disease grows constantly 
worse because no remedial measures are taken. 

Schistosoma japonicum vel cattoi. This species is common in China, 
Japan, and the Philippines. The disease produced by it is called 
Katayama disease. The liver hardens and the spleen enlarges. There 
is dysentery and loss of blood. The eggs are smaller than S. haemato- 
bium, and the species do not have the terminal spine. 

In Formosa, Paragonimus Westermani (Fig. 182), (Asiatic lung' 
fluke or bronchial fluke), is often found as a parasite infecting the lungs 
of man. It is also found in the brain where it causes death from 

The worm is from 8 to 16 mm. long and from 4 to 8 mm. broad, 
and is pinkish or red in color. The disease it causes is often confused 
with tuberculosis, although the microscope shows many eggs in the 
sputum. The liver, brain, and eyelid are the points most commonly 

The common liver-fluke, Fasciola hepatica, though rare in the United 
States, is common in Syria where men eat raw goat-livers. The disease 
is called Halzoun. 

Flatworms and Threadworms 


Opisthorchis (Distoma) felineus is common in cats. It has been 
found in Prussia, Siberia, and Nebraska. 

Opisthorchis noverca (Distomum conjunctum) is the Indian liver- 

Fig. 182. Infective Trematodes. 

I. Opisthorchis felineus. Os., oral sucker; Ph., pharynx; /., 
intestine; Vs., ventral sucker; ut., uterus; Vg., vitelline glands; 
Vd., vitelline duct; O., ovary; T., testes; Ec, excretory canal. 

II. Opisthorchis noverca. A., greatly enlarged. B., almost na- 
tural size, m., mouth (oral sucker); ph., pharynx; ac, acetabulum 
(ventral sucker); ut., uterus; vt., vitelline glands; ov., ovary; vd., 
vas deferens; t., testes; i., intestine; ex p., excretory pore. 

III. Fasciolopsis buski. 

IV. Heterophyes hcteropliyes. a., schematic and highly en- 
larged; b., about twice natural size; e., eggs, greatly magnified; 
d., spine greatly magnified. (I, after Stiles and Hassal; II, after 
Manson; III, after Rivas; IV, after Loose.) 

V. Paragonimus W ester mani (Asiatic Lung Fluke): 1, oral 
sucker; 4, intestine; 7, acetabulum; 8, ovary; 9, excretory canal; 
11, yolkglands; 12, testis; 14, uterus. (After Pratt.) 

Opisthorchis (Distoma) sinensis. This is one of the most important 
of liver-flukes. It occurs extensively in Japan, China, and India. It is 
from 10 to 20 mm. long and from 2 to 5 mm. broad. The eggs are oval 

294 General Biology 

and dark-brown, with sharply denned operculum. O. sinensis are also 
found in Canada and the United States. Children are usually affected, 
and whole villages succumb to its ravages. 

Fasciolopsis (Distoma) buski is common in India, and 

Mesogonimus heterophyes in Egypt and Japan. 


The common tapeworm, Taenia solium (pork tapeworm), (Fig. 183), 
is the best laboratory example of Cestoda. It lives in the digestive tract 
of man and feeds upon the already digested food of its host. The tape- 
worm, therefore, needs no digestive system of its own, and it has none. 

Taenia is a long flatworm consisting of a knob-like head, called the 
scolex, and a great number of segments which are all like each other but 
different from the scolex. These segments are known as proglottids. 

Hooks and suckers on the scolex permit the animal to fasten itself 
to the walls of the digestive tract of its host. A small .constriction 
between head and proglottids is called the neck. The proglottids usually 
increase in size the further they are from the scolex. It is not uncom- 
mon to have a tapeworm reach ten or more feet in length and have some 
eight or nine hundred proglottids. The proglottids are budded off from 
the neck, so that the segments furthest from the head are the older. 
The process of forming new proglottids is called strobilization. 

The body of the simplest type of tapeworm is not segmented, though 
most forms are. 

Each proglottid contains a set of both male and female reproductive 
organs, but the nervous and excretory systems are usually quite con- 
tinuous through head and proglottids. The question often arises as to 
whether each segment is not a complete individual, but the best authori- 
ties believe that the scolex is an asexual individual which buds off the 
sexual individuals which we have called proglottids. 

There are many species of tapeworms, but all live as parasites in 
the intestinal tract of other animals, and nearly all require two hosts 
before their life-cycle is completed. And, somewhat as the liver flukes 
require a cold-blooded and a warm-blooded animal as their hosts, so the 
tapeworms usually require some herbivorous animal as a host for the 
larval stages, and an animal which eats the flesh of the herbivorous 
animal for the adult stages. We, therefore, have tapeworms using pig 
and man, cow and man, fish and man, mealworm and rat, fleas and dog, 
rabbit and wolf, etc., as the two hosts. 

An adult tapeworm in the intestine of man will continually develop 
new proglottids which pass out of the body and shed the eggs upon the 
ground. Each proglottid may produce thousands of eggs. If these eggs 
then come in contact with grass, weeds, hay, or any vegetation which 
cattle or hogs eat, they hatch in the intestine of the animal eating such 
vegetation. In the case of the pork tapeworm, each Qgg will develop 

Flat worms and Threadworms 


Fig. 183. Tapeworms. 

A. The Life-History of Taenia solium. 1, six-hooked embryo in egg-case; 2, 
proscolex or bladder-worm stage, with invaginated head; 3, bladder-worm with 
eyaginated head; 4, enlarged head of adult, showing suckers and hooks; 5, general 
view of the tapeworm, from small head and thin neck to the ripe joints; 6, a ripe 
joint or proglottis with branched uterus; all other organs are now lost. 

B. A proglottis of Taenia solium with the reproductive organs at the stage 
of complete development. cs., Cirrus sac; excr., excretory canals; g.o., genital 
opening; n.c, nerve cord; ov., ovary; sh.g., shell gland; t., testes; v.d., vas 
deferens; ut., uterus; vag., vagina; y-g., yolk gland. 

C. Diagrams of Bladder- Worms. I. The Ordinary Cysticercus type, with one 
head. II. The Coenurus type, with many heads. III. The Echinococcus type, with 
many heads, and with blood capsules producing many heads. 

D. Portion of hog's liver infested with echinococcus bladder-worm. (A, after 
Leuckart; B and C, after Borradaile; D, after Stiles.) 

a little six-hooked embryo which leaves the egg and bores its way into 
the hog's body. It comes to rest either in the liver or muscle tissue. 

In about three months a bladder-w r orm known as a cysticercus has 
developed, and if flesh containing these bladder worms is eaten by man, 
he is in turn infected. 

The cysticercus is really a tiny bladder-like sac with a scolex pushed 
in on one side. When this gets into man's intestine, the scolex is pushed 
outward so that it can fasten its hooks into its new host's intestine. It 
is now ready to bud off proglottids again. 

At least one per cent of all cattle slaughtered in this country have 

296 General Biology 

tapeworms. Certain species are also found in pork. All meat should 
therefore, be well cooked before eating. 

The structure of the tapeworm is quite similar to Planaria, the flat- 
worm which served as our introduction to this phylum. 

It is well, however, to obtain a good description of the way tape- 
worms reproduce, as it is due to their reproduction that infection takes 
place. The mature proglottid is almost entirely filled with reproductive 
organs. From the spherical testes (which are scattered throughout the 
entire proglottid) the sperm cells are carried through the vas deferens, 
after being gathered into fine tubules, and pass to the genital pore. 

Eggs arise in the two-lobed ovary, and pass into the oviduct. Yolk 
from the yolk-gland then enters the oviduct and surrounds the eggs. 
After this, a shell is provided for the Qgg by the secretions from the shell- 
gland, and the eggs pass into the uterus. By this time the eggs have 
been fertilized and pass into the vagina. As the proglottid grows older, 
the uterus becomes extended with eggs and even sends off uterine 
branches likewise filled with eggs, while the rest of the reproductive 
organs are absorbed. The proglottid is then said to be ripe. When 
ripening occurs, the proglottid is very likely to break off and be thrown 
out with the faeces. 

Cestode Infections. 

There are four principal types of cestode worms (Fig. 184) which 
infect the human being. These are : 
Taenia saginata or mediocanellata, 
Taenia solium, 
Bothriocephalus latus, 
Taenia echinoeoccus. 

Each of these requires an intermediate host for the development of 
the larval forms. The eating of the flesh of the intermediate host releases 
the larval forms, and the mature worm forms in the human host. 

Taenia saginata (the common beef-tapeworm) is common in the 
small intestine of man in America. As the segments (which are loaded 
with eggs) ripen, they are discharged. The eggs are taken up with the 
food of the ox. Then the embryo pierces the intestinal wall with the 
four sucking discs on the worm's head. (There are no hooks in T. 
saginata.) As it bores its way through into the blood-stream, it is 
carried by the blood-stream throughout the entire system. Finally, the 
worm comes to rest in various muscles and develops into a cystic larval 
form. It is at this point that man becomes infected if raw beef is eaten 
which contains these larvae. 

Taenia solium has less uterine pouches filled with eggs than 
Taenia saginata. These eggs are ingested by pigs. This type of tape- 
worm is rare in the human intestine in the United States, although it 
does occur. The process of development is quite like that of Taenia 

Flatworms and Threadworms 


saginata. The cystic larvae of Taenia solium are called Cysticercus 

Bothriocephalus Latus is tound in many types of fish, such as sal- 
mon, trout, perch, etc., and, if this is ingested by man, it passes through 


Fig. 184. Types of Cestoda. 

I. Heads of 1, Taenia Solium; 2, T, Saginata; 3, Dibothrioccpltalus latus; 
4, Dipylidium caninum, this latter showing rostrum both evaginated and invagi- 
nated; 5, immature and 6, mature cysticercoid. (From various authors.) 
II. Diagram of the anatomy of Tapeworms. 1, Taenia saginata; 2, Dibothrioce- 
phalus latus. T, testes; Vol., vas deferens; C, cirrus; Gp., genital pore; Va., vagina; 
Rs., receptaculum seminis; Vtg., vitelline glands; Vtd., vitelline duct; Sg., shell 
gland; Ov., ovaries; Ovd., Oviduct; Ut., uterus; Ot., ootype; Exd., excretory duct; 
Mt., metraterm. (After Rivas.) 

the various stages already mentioned and produces considerable anaemia. 
The genital openings are on the face of each segment in Bothriocephalus 
latus instead of at the edges as in Taenia. 

Taenia echinococcus differs from the three forms just mentioned in 
that man is the intermediate host and the dog the true host. 


General Biology 

It also differs in size from those mentioned. Tapeworms in the 
human being may reach a length of thirty to forty feet, but Taenia 
echinococcus is only three mm. to six mm. in length. In cold countries 
where men and dogs live in the same room and where dogs lick their 
master's faces, eggs are transmitted to the human digestive tract, 
although intermediate hosts other than man are possible. 

The developing cyst in the instance of the small worm is very large, 
and there is a closely allied form known as Taenia multilocularis which 
often is present with Taenia echinococcus, and when this is the case, a 
great mass of ramifying spongy tissue, full of small cavities, forms. If 
these cysts grow in the brain, the sheer pressure of the cysts cause injury 
and then, too, if the first cyst ruptures, it pours out poisons into the sys- 
tem, as well as again spreading new larvae which form secondary cysts. 

The egg, when in the human intestine, hatches and bores through 
the intesinal wall and is swept along by the blood-stream to its lodging 
place. A thin, pearl-colored covering then surrounds it and about this 
the tissues of the host react so as to form a capsule. A liquid is formed 
in the thin membrane while buds grow out of the membrane. These 
buds are finally recognizable as the heads of new worms. The heads 
turn inside out, causing the hooks to face inward. This makes it possible 
for the worm to be swallowed by dogs and pigs. Then the head turns 
back again to make use of its hooks and suckers. If no intermediate 
host is found, the worms may die, but in such a case a large cyst filled 
with a mortar-like white material remains. Following is a summary 
of all the important tapeworms and their hosts : 

Taenia solium . 

Taenia saginata 

Taenia elliptica 

Taenia cucumerina 

(Both of these are also 
Dipylidium caninum 

Taenia flavo-punctata .... 
(Hymenolepsis diminuta) 

Taenia nana 

(Hymenolepsis nana) .... 

Taenia confusa 

Final Host 



Dog and cat mostly 
but also man 

Common in rats 

Twelve cases known 

in man. 
Common in Italy 

and known in 


A few cases in Man. 

Intermediate Host 
Hog (in liver, mus- 
cles, brain, and 
Ox and giraffe (in 

I n body - cavity o f 
dog, fleas and lice. 

Moths and beetles. 

Flat worms and Threadworms 


Dibothriocephalus latus . 

Drepanidotaenia setigera 

Man and Dog 

Common in Fin- 
land and regions 
where fish is a 
common food. 

In peritoneum and 
muscles of pike, 
perch, and trout. 

Water-flea and 
Cyclops brevicau- 



The nematodes are the threadworms, or round worms, which make 
up the phylum Nemathelminthes. 



Fig. 185. A Cross Section, Ascaris Lumbricoides. 

A, Transverse section, cm., cuticle; dl., dorsal line; der.epthm., epidermis; ex.v., 
excretory tube; int., intestine; lat. L, lateral line; m., muscular layer; ovy., ovary; 
ut., uterus; v.v., ventral line. 

B. A female cut open to show internal structures. 1, pharynx; 2, intestine; 
3, ovary; 4, uterus; 5, vagina; 6, genital pore; 7, excretory tube; 8, excretory pore. 
(A, after Vogt and Yung; B, after Shipley and MacBride.) 

This phylum is likely to prove confusing to students as there are 
various systematists who classify threadworms under different phyla 
and under groups which they call "uncertain." 

Nematodes form the single class of Nemathelminthes, and the tw r o 
best known forms used in the laboratory are Ascaris lumbricoides (Figs. 
185 and 186), a parasitic worm found in the digestive tract of pigs, horses, 
and man, belonging to the family Ascaridae; and Trichinelia spiralis 


General Biology 

(Fig. 187), of the family Trichinellidae, which causes a very dangerous 
disease called trichinosis in rats, pigs, and man. 

The female Ascaris is the larger of the sexes; in fact, it may grow 
to a length of from five to eleven inches and a quarter of an inch in 
diameter. The body is of a light brown color, with a narrow white 
stripe along the dorsal and ventral surface, and a broader white line 

Fig. 186. Tuberculous Cavity in Oesophageal 
Wall of Man Containing an Ascaris 
Lumbricoides. (From a photo- 
graph lent the author by 
Dr. E. L. Miloslavich.) 

Fig. 187. Trichinella Spiralis. 

A. Encysted Trichina Embryo. 

B. Adult female from Intestinal wall. 1, 
parasite; 2, membrane of cyst; 3, muscle-fiber 
of pig. (After Leuckart.) 

lying on each side of the dorsal and ventral stripe. 

The mouth-opening (which is surrounded by one dorsal and two 
ventral lips) lies at the anterior end of the animal. The anal opening 
lies at the posterior end. The tail-end of the female is straight, while 
in the male it is slightly bent. In the male also there are penial setae, 
which extend through the anal opening and which are used for copu- 

The Digestive System. 

The digestive system is very simple, consisting of a mere straight 
tube into which the already digested food of the host enters. A definite 
coelom may also be seen. The more anterior portion of the digestive 
tube is known as the pharynx. This is muscular, so that by contraction 

Flatworms and Threadworms 301 

and expansion it can draw the host's food into itself. At the posterior 
end of the digestive tube the intestine becomes smaller. This is the 
rectum, which empties through the anal opening. 

The Excretory System. 

This system consists of two longitudinal canals, one located in each 
lateral line. These open through a single pore near the anterior end of 
the ventral body-wall. 

The Nervous System. 

A definite ring of nervous tissue surrounds the pharynx. From this 
ring a dorsal and a ventral nerve cord are given off, as well as a number 
of fine nerve strands and connections. 

The Reproductive System. 

In the male there is but a single testis, which is coiled and thread- 
like. The sperm cells pass from this through a vas deferens to a seminal 
vesicle and from here through the ejaculatory duct to the rectum. 

In the female the reproductive system is Y shaped, the two arms 
of the Y being the coiled ovaries which are continuous with the uterus. 
It is the two uteri which unite in the stem of the Y to form a muscular 
tube, the vagina, which opens to the outside of the body by a genital 

The egg is fertilized in the uterus, after which a chitinous shell 
surrounds it, and the egg is then thrown out through the genital pore. It 
is this chitinous shell which prevents the egg from being digested in 
the intestine of the host where it must necessarily fall when laid. 

As nematodes are triploblastic animals with three definite germ 
layers, these animals also have a coelom. Consequently, the body of 
these worms must be thought of as a tube within a tube, with the repro- 
ductive system lying between the digestive tract and the body wall — 
that is, within the coelom. 

However, the coelom is quite different in worms from what it is 
in higher animals. In the higher forms, the coelom is a cavity between 
the two layers of mesoderm. The excretory organs open into it and 
from its walls the reproductive cells originate. In Ascaris the coelom 
has only the mesoderm of the body wall as a lining. There is no meso- 
dermal lining surrounding the intestines. Then, too, the excretory or- 
gans open directly to the outside through the excretory pore, and the 
reproductive cells do not originate from the epithelium of the coelom. 
Notwithstanding this difference, the space between the intestinal tract 
and the body wall is called coelom in worms. 
Nematode Infections (Figs. 185, 186, 187, 188). 

Ascaris lumbricoides is found chiefly in children. The female is 
from seven to twelve inches in length, and the male from four to eight 
inches. The worm is pointed at both ends and of a yellowish-brown or 


General Biology 

Fig. 188. 

Oxyuris Vermicularis 

The male is on the left, the 

female on the right. 

(After Claus.) 

Fig. 189. Eggs of the More Important Worms Which Are 
Parasitic to Man. 

As all are of the same magnification, a comparison of the rela- 
tive sizes is possible. 

1, Fasciolopsis buskii; 2, Schistosoma mansoni; 3, Schistosoma 
haematobium; 4, Schistosoma japonicum; 5, Paragonimus wester- 
manii; 6, Clonorchis sinensis; 7, Metagonimus yokogawai; 8, Taenia 
saginata; 9, Taenia solium; 10, Hymenolepsis nana; 11, Hymeno- 
lepsis diminuta; 12, Diphylloboth'rium latum (Dibothriocephalus 
latus) ; 13, Ascaris lumbricoides (egg without outer coating); 14, 
Ascaris lumbricoides (abnormal egg); 15, Ascaris lumbricoides; 16, 
Trichuris trichiura, 17 and 18, Hookworm eggs; 19, Enterobius 
vermicularis oxyuris vermicularis ; 20, Oxyuris incognita; 21, Tricho- 
strongylus orientalis. (After Hegner and Cort's "Diagnosis of Pro- 
tozoa and Worms Parasitic to Man." Bull. Johns Hopkins Uni- 
versity School of Hygiene and Public Health.) 

slightly reddish color. There is no intermediate host. The animal 
occupies the upper portion of the small intestine. Usually one or two 
are found in a single location, although sometimes vast numbers of 
them may be found. The worm may pass to the stomach and be 

Flatworms and Threadworms 303 

vomited forth, or it may crawl up the oesophagus and then pass into 
the larynx and asphyxiate the patient. In fact, it may enter any ducts 
or tubes in the body. 

Oxyuris vermicularis (commonly called pin-worms 
or thread- worms), (Fig. 188), are parasites of the rec- 
tum and colon. The male is about 4 mm. long and 
the female about 10 mm. The parasites migrate and 
come close to the surface during the night, thus caus- 
ing accentuated irritation and itching about the rec- 
tum and genital organs. Many eggs are found in the 
faeces of infected children. It is essential that the dis- 
Fig - 19 °- tinguishing and diagnostic difference between oxyuris 

a., e mai°e°; °b™ fe- e gg s an d trichocephalus eggs be known. Both types 
^p a eniW 'ford*s h c'har^e are <l uit ? alike exce Pt that trichocephalus eggs have a 
of e gg s - (After button-like lighter area (Fig. 189, 16). Re-infection 
must be guarded against. These worms often find 
their way into the appendix of children where they drill into the mucous 
membrane and cause appendicitis. Trichina (Fig. 187), (also called 
Trichinella spiralis), lives in the small intestine when adult. The disease 
trichiniasis is caused by the embryos after they pass from the intestines 
to the voluntary muscles where they encapsulate themselves as larvae. 

The female is 3 to 4 mm. long and the male 1.5 mm. There are two 
tiny projections from the posterior end of the worm. The larvae, when 
encased in the muscle, are about 1 mm. long. Trichina has a pointed 
head and a somewhat rounded tail. The parasites are ingested by man 
when eating inadequately cooked pork. Each worm may produce as 
high as 10,000 young, which are either placed directly into the lymphatics 
by the female or burrow through the intestinal wall. They then encyst 
in the muscle tissue. Pigs acquire the disease by eating offal or infected 

Twenty-six different kinds of animals have been found to harbor 
trichinae, and as many as 15,000 of these parasites have been found in 
one gram of muscle. 

It may take about six weeks for complete encapsulation, but once 
encapsulated, they may remain alive in the muscle for twenty or twenty- 
five years. 

Pigs may be literally "filled" with these parasites, although they 
may show no external sign of infection. The result is what is known 
as "measly" pork. Many countries now insist on pork inspection to 
prevent a spread of infection. 

The patient usually suffers with a fever, anaemia, muscle pains 
(myositis), which are often mistaken for rheumatism, and intestinal 
disturbances (gastro-enteritis) . 

Ankylostoma duodenale in the old world, and Necator americanus 
in this country are the Hook-worms (Fig. 190). The disease caused 
by hook-worm is variously known as ankylostomiasis, uncinariasis, 


General Biology 

hook-worm disease, tropical 
or Egyptian chlorosis, and 
anaemia of bricklayers and 

The old-world animal is 
small and cylindrical, the 
male being about 10 mm. in 
length and the female from 
10 to 18 mm. There are 
chitinous plates about the 
mouth and there are two 
pairs of sharp, hook-shaped 
teeth with which the mucosa 
of the intestine is pierced. 
On the male there is a prom- 
inent caudal, umbrella-like 
expansion. The American 
species is slightly more slen- 
der, with a globular mouth 
and a different arrangement 
of teeth. The eggs of the 
American form are slightly 
larger than those of the 
European forms. 

The larvae of the hook- 
worm develop in moist earth 
and dig their way through 
the soles of the feet of per- 
sons who go barefooted. 
Once in the blood-stream, 
they are carried along by it 
to the heart, thence to the 
lungs. Many lodge in the 
windpipe from whence they 
are swallowed, thus reach- 
ing the stomach and intes- 
tines. The larval forms here 
attach themselves to the in- 
testinal walls and feed on 
the blood of their host. But 
as they puncture the intestinal wall, they exude a small amount of 
poison which prevents the host's blood from coagulating. There is 
thus a constant loss of tiny droplets of blood and the patient naturally 
becomes anaemic. Not only do persons infected with hook-worm suffer 
from such loss of blood, but the parasites injure' the lungs in passing 
through them, and thus make tuberculosis infections easy. 

Forms of Worms Parasitic to Man. 

1. Larval stage of Filaria ozzardi (F. demarquayi). 

2. Larval stage of Loa loa (Microfilaria diurna). 

3. Larval stage of Filaria bancrofti (Microfilaria 

4. Larval stage of Acanthocheilonema perstans (Mi- 
crofilaria perstans). 

5. Adult parasite female of Strong yloides stercoralis. 
6 ad 7. Adults, male and female, of the free-living 

generation of Strongyloides stercolaris. 

8. Rhabditiform larva of Strongyloides stercoralis, 
just hatched from egg. 

9. Filariform infective larva of Strongyloides ster- 

10. Rhabditiform larva of Ancylostoma duodenale, 
just hatched from the egg. 

11. Filariform infective larva of Ancylostoma duo- 
denale. (From Hegner and Cort's "Diagnosis of Proto- 
zoa and Worms Parasitic to Man;" 1-4, after Fulleborn; 
5-11, after Looss.) 

Flatworms and Threadworms 


Fig. 192. Elephantiasis in Man 

(From "New Sydenham 

Society's Atlas.") 

The writer has been told by a worker in 
the medical corps of the army that more than 
75 per cent of the examined southern negroes 
showed hookworm infection. 

It is of great importance to dispose of all 
human faeces in rural districts, in mines, brick- 
yards, etc., so that the soil will not become 
polluted. This will at the same time kill, the 
eggs and thus prevent their hatching. Strong 
sunlight also seems to be quite effective in 
killing such eggs. 

The family Filariidae is also important 
from a pathological point of view. 

Filaria bancrofti (Fig. 191) is a parasite 
which lives in human blood. It is interesting 
to know that this parasite lives in the lungs 
and larger arteries throughout the day and in the blood vessels in the 
skin at night. Mosquitoes, which are active at night, suck the blood of 
infected persons and thus carry the infection. In fact, it was the knowl- 
edge of this peculiarity of Filaria bancrofti which led to the discovery 
of the malarial parasite's life cycle. 

After the larvae have developed in the mosquito's body, the 
organisms are placed in another person by the mosquito. They enter the 
lymphatics and cause serious difficulties, probably by blocking the lymph 
passage. If there is such a blocking, elephantiasis results. This is a 
practically incurable disease in which the limbs, or other portions of the 
body, swell to an enormous size, although producing little or no pain. 
(Fig. 192.) In certain portions of the South Sea Islands, almost a third 
of the population is affected. 

Medical men speak of Filaria diurna and Filaria perstans. The first 
of these differs from F. bancrofti in not having granules in the axis of 
the body, and the second in having embryos smaller (namely, about 
200 microns) than the preceding. Only the embryos have been seen. 
The embryos of F. bancrofti are about 270 to 340 microns in length. 
The adult is about 83 mm. long, and the female some 155 mm. The tail 
in the male has two spiral turns. The female produces vast numbers 
of young which enter the blood stream through the lymphatics. Each 
embryo is inclosed in a tiny shell, about one ninetieth of an inch in 
length. They pass through the capillaries quite readily. They can be 
seen in a blooddrop under the microscope. As many as 2,100 embryos 
have been seen in 1 cc. of blood. 

Dracunculus medinensis is a peculiar worm, the female of which is 
about a yard long. It is probably taken in with food. It makes its way 
downward, and, when arriving at the ankle, usually pushes its head 
through the skin, causing an abscess. As the eggs are then deposited, it 


General Biology 

Fig. 193. Other Nematode Parasites. 

I. a., Dracunculus (filaria) medinensis (female), showing mouth and embryo. 
b., Transverse section through adult female of I, a, showing many embryos 
in the uterus. 

II. Cyclops. This animal is the intermediate host of Dracunculus. 

III. Trichocephalus dispar (also called Trichuris trichiura) of the Family 
Trichinellidae. a., egg; b., female; c, male attached to the intestine, showing the 
long, slender, cephalic end buried in the submucosa; sp., spicule. 

IV. Gigantorhynchus gigas, of the Class Acanthocephala, and Family Echinor- 
hynchidae. A., two males and one female adult attached to the mucosa of the 
intestine; B., eggs as seen in preparation; C, eggs as found in feces. (I, after 
Bastian and Leuckart; II, after Riley and Johannsen; III, after Leuckart; IV, 
after Brumpt and Perrier.) 

leaves the infected person of its own accord. Few of these have been 
found in America. 

Trichocephalus dispar (Fig. 193), or whip-worm, is found in the 
caecum and large intestine of man. It is 4 to 5 cm. in length, the male 
being a trifle shorter than the female. The parasite is remarkable in 
that there is a great differentiation between the two ends of the body. 
The anterior end, which forms about three-fifths of the body, is very 
thin and hair-like, while the posterior portion is thick. In the female, 

Flatworms and Threadworms 307 

the posterior end is conical and pointed ; in the male, it is blunter and 
rolled like a spring-. The eggs are lemon-shaped, 0.05 mm. in length. 
Each has a button-like projection. There may be as many as a thousand 
parasites in one person. The parasite produces no known symptoms in 
the patient, although patients who have been infected have become 
anaemic and suffered with diarrhoea. 

Dicotophyme renale is a worm, the male of which is over a foot 
long and the female over three feet. These are seldom met with, but 
when present may destroy the entire kidney. 

Anguillula aceti or (vinegar eel) has been found in the urine of man, 
although it is supposed to have been in the bottle in which the urine was 

Strongyloides intestinalis is found in the small intestines of man in 
the tropics. Three per cent of the medical patients of the Isthmus of 
Panama were found to be infected, and 20 to 30 per cent of the insane 

Acanthocephalus (thorn-headed) is also called Gigantorhynchus or 
Echinorhynchus. These are quite common in the intestine of the hog, 
where they attach themselves by means of a protrusible proboscis 
covered with hooks. In the old world the larva develops in cockroach 
grubs, while in America the larva develops in the June bug. 

The Acanthocephalia are distinguished from the Nematodes and 
the Nematomorpha by the presence of a proboscis and the absence of an 
alimentary canal. 


In addition to the rather definite groups of worms mentioned in this 
book, there are also various forms of uncertain position. 

The term Mesozoa (Fig. 194) — (Gr. mesos, middle — zoon, animal) — 
is often used as a general grouping for the three following families of 
parasites: (1) Dicyemidae, (2) Orthonectidae, (3) Heterocyemidae. 

They are called Mesozoa because they are regarded as intermediate 
forms between the protozoa and the metazoa. They are closely allied 
to the flat worms. 

The Nemertinae (Gr. nemertes, true), are usually placed with the 
flat worms. They may reach a length of ninety feet and are mostly 
marine, though a few live in fresh water and in moist earth. 

Cerebratulus ( ), and Micrura ( ), 

(Fig. 195), are the usual examples of marine Nemertinae. Other forms 
are not common. Malacobdella ( ) is parasitic in 

some mollusks. 

The Nemertinae are considered the lowest form of animal life in 
which the blood-vascular system appears. There is a definite mesoderm 
and a nervous and an excretory system quite like those in flatworms, 
but they all have a long proboscis just above the digestive tract which 
lies within a sheath. This can be everted. The body is covered with 


General Biology 

Fig. 194. 

A. A Mesozoon, 
Dicyema Paradoxum. 

(From Parker and 

Haswell, after 


B. A Mesozoon, 
Rhopalura giardii, 


(From Sedgwick, 

After v. Beneden.) 

C D Fig. 

A. Malacobdella grossa (Ver- 
rill), entire worm. 1, proboscis; 
2, mouth; 3, intestine; 4, 

B. Section through forward 
end. 1, mouth; 2, proboscis; 3, 
proboscis sheath. 

C. M (crura leidy, (Verrill.) 

D. Cerebratulus lacteus (Ver- 
rill). (From Pratt's "Manual" 
by permission of A. C. McClurg 
& Co.) 

195. E 

E. Cerebratulus fuscus, a Ne- 
mertine. 1, cephalic slits; 2, 
opening leading into retracted 
proboscis; 3, dorsal commis- 
sure of nervous system; 4, 
ventral commissure; 5, brain; 6, 
posterior lobe of brain; 7, 
mouth; 8, proboscis; 9, lateral 
vessel; 10, proboscis; 11, 
pouches of alimentary canal; 12, 
stomach. (From Shipley and 
MacBride, after Burger.) 

cilia. These animals feed on other animals both dead and alive. They 
usually live in burrows of mud and sand, though Cerebratulus is free- 

A peculiar larval stage known as the Pilidium (Fig. 198 D), 
resembling a helmet with cilia and a long tuft at the apex, is a dis- 
tinguishing feature of the development of Nemertinae. Ectodermal 
invaginations surround the alimentary tract of the Pilidium. This 
invaginated portion escapes from the larval form and becomes an adult. 

The Nematomorpha (Gr. nema, thread — morphe, form), is made up 
of the single family Gordiidae (Fig. 196). These are the common horse- 
hair snakes. Various authors classify them under the order of Nema- 
toda, while others classify them under the Phylum Nemathelminthes. 
There are two genera : Gordius, which lives in fresh water, and Necto- 
nema, a marine form. The internal anatomy is somewhat different from 
the Nematodes, as there is a distinct epithelium lining the body cavity 
and no lateral lines. There is also a pharyngeal nerve-ring, and a single 

Flatworms and Threadworms 



Fig. 196. 

I. Gordius aquaticus ; hinder end of male. 

II. Gordius lineatus ; hinder end of male. 

III. Paragordius varius; A, hinder end of female; 
,, ™ V - Nectonema agile; (From Pratt's "Manual' 
McClurg & Co.) 


B, of male, 
by permission 


of A. C. 

A. B. Two species of Rotifera. A, Philodina. B, Hydatina. 
(From Parker and Haswell, after Hudson and Gosse.) 

C. Diagram showing the anatomy of a Rotifer. a, anus; 
br, brain; c\ preoral, and c 2 , postoral circlet of cilia;, ce- 
ment gland; cl, cloaca; d.ep, dermic epithelium; d.f, dorsal 
feeler; e, eye; fl.c, flame-cells; int, intestine; m, muscles; mth, 
mouth; nph, nephridial tube; ov, ovum; ovd, oviduct; ovy, ger- 
marium; ph, pharynx; st, stomach; vt, vitellarium. (From 
Parker and Haswell.) 

D. Philidium larva of a Nemertine. D, alimentary canal; 
E, E', the two pairs of ectodermal invaginations. (From 
Sedgwick, after Metschnikoff.) 

Fig. 197. 
The arrowworm, Sagitta hexap- 
tera (of the group Chaetognatha), 
ventral view, a, mouth; b, intes- 
tine; c, anus; d, ventral ganglion; 
e, movable bristles on the head; f, 
spines on the head; g, ovary; h, 
oviduct; i, vas deferens; j, testis; 
k, seminal vesicle. (After Hert- 


General Biology 



Fig. 199. 

Bugula avicularia, a Brjozoon. Av, 
; D, alimentary canal; F, funiculus; 
Oes, oesophagus; Ovz, ovicells; R, retractor 
muscle; Te, tentacular crown. (From Sedg- 
wick, after V. Nordmann.) 

B. Phoronis architecta. Young individ- 
ual with about 30 tentacles. 1, epistome; 2, 
lophophore; 3, digestive tract. (From Pratt's 
"Manual" by permission of A. C. McClurg 
& Co.) 

ventral nerve-cord, while the ovaries 
discharge the eggs into the body- 
cavity. Then, too, the larvae of 
Gordious usually enter immature 
stages of aquatic insects. These in- 
sect larval-forms are then devoured 
by other animals, and it is in the 
intestines of the host where they de- 
velop until they finally escape into 
the water. 

The Acanthocephala ( G r. 
akantha, spine — kephale; head) are 
the parasitic worms already men- 
tioned above (Fig. 193), which may 
infect man. They fasten themselves 
to the intestinal wall of their host 
by means of a protrusible proboscis 
covered with hooks. In fact, it is 
the presence of the proboscis and a 
reproductive system as well as the 
absence of an alimentary system which distinguishes the Acanthocephala 
from the Nematoda and the Nematomorpha. There is an alternation of 
hosts during the developmental stages. 

The Chaetognatha (Gr. chaite, horse-hair+gnathos, jaw) are marine 
forms swimming about near the surface of the water. The arrow-worm 
(Fig. 197) is the classic example. This is a member of the genus Sagitta. 
The Chaetognatha are quite often included under the Phylum Nemathel- 

The Rotifera or Rotatoria (Fig. 198), (Lat. rota, wheel-fero, I 
carry), are usually called the wheel-animalcules. They are very small 
and were formerly thought to belong to the Infusoria. Most of them 
live in fresh water. A few are parasitic. The sexes are separate. 
Summer and winter eggs are produced by the female. The former are 
thin-shelled and develop without fertilization (parthenogenetically). 
The larger eggs produce only females while the small eggs reproduce 
males. The winter eggs are fertilized, have thick shells, and all develop 
into females. The eggs of the most mollusks pass through a larval stage 
known as a trochophore ( ), which looks quite like 

the helmet-shaped larva described above. Now, Rotifers often resemble 
these trochophores. Consequently, it is thought by some zoologists that 
they must be closely related to the mollusks. Rotifers have a peculiar 
ability to secrete about themselves in times of drought a gelatinous 
envelope, which protects them for great lengths of time and thus prevents 
them from perishing. 

The Bryozoa (Gr. Bryon, moss — zoon, animal) are moss-animals 

Flatworms and Threadworms 311 

(Fig. 199), which practically all live a colonial life. They look something 
like the hydroid form of Obelia, but their general structure is quite 
unlike Obelia. Most of them are marine animals, though there are a few 
types which inhabit fresh water. Polypide is the name given to the 
soft parts which lie within a coelomic cavity and which is surrounded 
by the zooecium (body-wall). 

The lophophore ( ) is the crown of ciliated 

tentacles surrounding the mouth. The alimentary tract, retractor mus- 
cle, and the funiculus (a strand of mesodermal-tissue attached to. the 
stomach), are shown in Figure 199. There are no circulatory or excre- 
tory organs. The eggs develop in the ooecium, which is a modified 
portion of the body-wall. 

Bugula is the usual laboratory example. Certain members of a 
colony develop jaws for protective purposes. Such jaw-possessing 
members are called aviculariae. 

Bryozoa are divided into Ectoprocta in which the anus opens out- 
side the lophophore, and a coelom is present as in Bugula; and Ento- 
procta, in which the anal opening lies within the lophophore, while the 
portion which should be a coelom is filled with mesodermal cells. 
Examples of this type are Pedicellina and Urnatella. 

The Phoronidea, named after an ancient king, Phoronis, consists 
of the single genus Phoronis. The animals belonging to this group are 
worm-like and are enclosed in membranous tubes. They live in sand 
and are supposed to be related to the Ectoprocta. 

The Brachiopoda (Gr. brachion, arm — pous, foot) are shelled marine 
animals (Fig. 200), but with the shell on the dorsal and ventral portions 
of the animal, instead of on the sides as with bi-valves. They are usually 
attached to some object by a peduncle. An excellent example is Lingula, 
a very old type, which has been found in some of the oldest geological 
strata, and which differs but little to-day from the oldest fossil-remains. 

The Brachiopoda are not worm-like in any way, but have an 
uncertain position in classification, and so are included here. 

The Gephyrea (Fig. 201), (Gr. gephyra, mound), often classified 
under the annelids, are now believed by zoologists to be unrelated to 
them, but there is even doubt that the various sub-groupings of 
Gephyrea themselves bear any very close relationship. 

Three groups are usually mentioned : 

(1) The Echiuroidea, in which the adult shows traces of segmenta- 
tion, a proboscis, and a pair of ventral-hooked-setae and terminal anus. 
There is a larval trochophore stage. They ordinarily live in crevices 
of rocks. 

(2) The Sipunculoidea are unsegmented. They possess one pair 
of nephridia, a large coelom, and an anal opening on the dorsal surface, 
near the head-end. They usually possess tentacles at the anterior end. 
They live in sand or bore their way into coral rock. 

(3) The Priapuloidea are also unsegmented, having an anterior- 


General Biology 

mouth surrounded by chitinous teeth and the anal opening in the pos- 
terior region. They live in mud and sand. The head-end usually pro- 
jects above the surface of the mud in which they lie. 

Fig. 200. 

Magellania fiavescens (of the group 
Brachiopoda). A, dorsal aspect of shell. B, 
shell as seen from the left side, b, beak; d.v., 
dorsal valve; /, foramen; v. v., ventral valve. 
(From Weysse, after Davidson.) 

Anatomy of a Brachiopod, Waldheimia 
australis. 1, mouth; 2, lophophore; 3, stom- 
ach; 4, liver tubes; 5, median ridge on shell; 
6, heart; 7, intestine; 8, muscle from dorsal 
valve of shell to stalk; 9, opening of nephrid- 
ium; 10, stalk; 11, body-wall; 12, tentacles; 
13. coil of lip; 14, terminal tentacles. (From 
Shipley and MacBride.) 

Fig. 201. 

A. Echiurus pallassi (of the group 
Gephyrea). a, mouth at the end of the grooved 
proboscis; b, ventral hooks; c, anus. (From 
the Cambridge Natural History.) 

B. Sipunculus nudus (of the group 
Gephyrea) laid open from the side. A, anus; 
BD, brown tubes (nephridia) ; D, intestine; 
G, brain; Te, tentacles; VG, ventral nerve- 
cord. (From Sedgwick, after Keferstein.) 

C. Priapulus candatus (of the group 
Gephyrea). a, mouth surrounded by spines. 
(From the Cambridge Natural History.) 

References : 

Ward and Whipple, "Fresh Water Biology." 

Hegner's "College Zoology." 

Pratt's "Manual of the Common Invertebrate Animals." 

Braun & Liihe, "A Handbook of Practical Parasitology." 

W. H. MacCallunn, "A Text-book of Pathology." 

Damaso Rivas, "Human Parasitology." 

Kolle & Wassermann, "Hand-buch der Pathologenen Mikroorganis- 

Hegner & Coit, "Diagnosis of Protozoa and Worms Parasitic in 

Needham and Lloyd, "The Life of Inland Waters." 

James G. Needham, "A Guide to the Study of Fresh-Water 



AS AN example of a gill-breathing- arthropod, the crayfish has 
become the classic laboratory type, and this because, like the 
frog, it is already known to the student to some extent. 

The phylum to which man and the frog belong — the Vertebrate — 
is in point of numbers much smaller than the phylum Arthropoda, to 
which the crayfish belongs — a group embracing more than three-fourths 
of all living animals. 

The Arthropoda are usually divided into branchiata 1 ( ) 

— commonly called Crustacea ( ) — those animals 

possessing a hard chitinous ( ) exoskeleton and 

breathing with gills, practically all of which live in water ; and tracheata 
( ), consisting of those animals breathing through 

little tubules called tracheae. The tracheata include grasshoppers, bees, 
wasps, ants, spiders, and insects of all kinds. While 400,000 of the 
600,000 known species of animals belong to the Arthropoda, the greatest 
sub-group of these is, in turn, the insects. 

The crayfish is large enough to be studied profitably in the labora- 
tory. All who have lived or spent any of their youth near ponds and 
rivers, know at least one or two species of crayfish. These they have 
found lying quietly under stones in running streams, and when such 
stones were lifted, the animal's pincers were threateningly brought for- 
ward to clasp the fingers of the supposed attacker." Then followed a 
darting backward until the animal again pushed itself under some shel- 
tering object or was able to find some close corner in which its body 
could be pressed. 

The exterior skeleton so prominent in the arthropoda, is in thorough 
contrast to that of the frog, whose supporting tissues are placed on the 
innermost portion of its body; yet it is not from this characteristic 
that the phylum is named, but from the fact that the animals belong- 
ing to this group have jointed legs. The word arthropoda means jointed 

The crayfish will be used in this book more as a type to introduce 
nomenclature and general arrangement of the phylum arthropoda than 
as a study of detail. 

The entry into a more minute investigation of the phylum will come 
with a study of the grasshopper. The larger and more convenient size 

^his classification into Branchiata and Tracheata lacks scientific foundation, but is convenient 
for the beginner and for the student of medicine. As an example of why this classification is not 
scientific, we may mention the fact that true spiders have no tracheae and yet are called Tracheates. 

314 General Biology 

of the crayfish serves to show in gross much that is otherwise difficult 
to observe in the insects and lends itself well to an illustration of serial 
homology and the so-called Savigny's law. The crayfish has not been 
well studied, unless, after completing this chapter, these things are 
definitely known. 


The crayfish is found nearly everywhere in this country and Europe. 
In the eastern part of the United States Cambarus affinis ( 
is prevalent, while Cambarus virilis ( ) is more plentiful 

in the middle states, and the European specimen found most frequenly 
is Astacus fluviatilis ( ). There is little difference, 

however, in the external or internal makeup of the different species. It 

Fig. 202. The common Crayfish, Astacus fluviatilis, seen from 
the side. 

abd. Abdomen. amb. 1. First walking leg. amb.. 4. 
Fourth walking leg. an'. First antenna or antennule. an". 
Second antenna. be. Branchiostegite. br.c. Branchiocardiac 
groove. ' c. Carpace. ch. Chela, cv.g. Cervical groove, e.s. 
Eye-stalks. gg. Opening of green gland. mxp. 3. Third 
maxillipede. rs. Rostrum. sw. Swimmerets. t. Telson. 15. 
First segment of abdomen. 20. Last segment of abdomen. xx. 
The last appendage. (After Shipley & MacBride.) 

will be remembered that the segmentation of the frog is found in the 
spinal column. With the crayfish, segmentation can be observed 
externally, running from anterior to posterior end, though there is a 
peculiar condition of fusing of a number of the anterior segments (Fig. 
202) which form the cephalothorax ( ). 

As one may observe in the embryological study of the crayfish that 
each embryonic segment possesses a pair of appendages, it is but neces- 
sary to count the appendages in an adult arthropod in order to find how 
many segments have fused in any given region. This is known as 
Savigny's Law. 

Beginning at the anterior end of the animal we find that the first 
segment has two pairs of long feelers, the longer ones being the antennae 
and the shorter the antennules. 

Directly behind these there is a series of modified appendages (Figs. 
202, 203). The larger pair are the mandibles, which cover the mouth 
itself. Two pair of tiny appendages — the maxillae — lie posterior to the 
mandible, while three pairs of appendages — the maxillipeds— posterior 

The Arthropoda 


to the maxillae (really attached to the thorax) are so modified that they, 
too, belong to the mouth formation. The two pair of maxillae' and the 
three pair of maxillipeds, together with the mandible, thus make six 
pairs of jaws altogether. 

Back of these six pairs of jaws, a pair of pincers is attached to the 
thorax proper. These are known as chelipeds ( ), 

and behind the chelipeds are four pair of walking legs. By observing 
these legs it will be noticed that they are very much akin to the cheale 
proper in that each has a broad attachment where it meets the body, the 

A. Mandible. B. First maxilla. C. Second maxilla. 
bs. Basipodite. ex. Coxopodite. en. Endopodite. ep. Epipodite. 
ex. Exopodite. sc. Scaphognathite. 

D. and E. First and second Maxillipedes. br. Branchial 
filaments. cp. Carpopodite. dp. Dactylopodite. is. Ischiopodite. 
me. Meropodite. prp. Propodite portions of endopodite. 

F. Third Maxillipede. cs. Coxopodite setae. 

G. Gill (—epipodite.) (After Latter.) 

protopodite ( ), composed of two portions, a coxopodite 

( ) and a basipodite ( ) which 

then join the pincer proper. These pincers consist of a solid immovable 
portion, the exopodite ( ) and a smaller movable and 

inner portion, the endopodite ( ). 

It will be observed that the pincers are only enlarged walking legs. 

The portion of the crayfish directly behind the cephalothorax, with 
the definite segmentation, is known as the abdomen and consists of six 
segments, beside the tail. The tail consists of a central portion 
called the telson ( ), and two pairs of leaf -like 

structures on each side called uropods, which assist in forming a broad 
wing-like tail and which, when the crayfish is frightened, can be bent 

316 General Biology 

rapidly forward, thus sending the animal's body backward trom the posi- 
tion it occupied. 

A typical segment of the abdomen (Fig. 204) consists of the upper 
portion called the tergum ( ), a ventral portion, 

the sternum, two pleura (the extended portions continuing ventrally be- 
hind the sternum), and two epimera, these latter forming the roof which 
extends from the pleura to the appendage. 

Fig. 204: 

A. Diagram of skeleton of an abdominal segment of Astacus. 
bs. Basipodite. ex. Coxopodite of swimmeret. ep. Epimeron. jt. 
Point of articulation with skeleton of adjacent segment. pi. 
Pleuron. st. Sternum, tg. Tergum. (After Latter.) 

B. Section through cephalothorax of a crab. (After Pearson.) 
H., Heart; Te., extension of the tergum; ST., sternum; PL., 
pleuron; T., tendons; 1st W. L., insertion of first walking leg; Br., 
gill in gill-chamber; g., gut; d.a., descending artery; A., afferent 
branchial; E., efferent branchial. 

There are thirteen segments in the cephalothorax. The eyes are 
not counted as appendages. A cervical groove forms the separating line 
between head and thorax. The entire dorsal shield of the cephalothorax 
is called the carapace ( ) ; the jointed end extending 

between the eyes is known as the rostrum, while the portion on the 
sides covering the gills are the branchiostegites ( ). 

The entire crayfish possesses twenty segments, counting telson and 
uropods as one. 

Each pair of the appendages is slightly different in appearance from 
any other pair, though there is much similarity between them. The 
three distinguishing types of crayfish appendages are known as (1) 
foliaceous ( ), (second maxilla); (2) biramous 

( ), (swimmerettes) ; (3) uniramous ( ), 

(walking legs). 

The female has an opening at the base of the third walking leg 
through which eggs are extruded. She also possesses a single opening 

The Arthropoda 317 

in the midline through which sperm may be inserted. Immediately be- 
hind the left walking leg, on the first abdominal segment, a peculiar 
atrophied ( ) pair of appendages is found. 

In the male, however, these appendages on the first and second ab- 
dominal segment are wide, and the left walking leg possesses a small 
opening through which the sperm are ejected. In the male the first pair 
of swimmerettes is also transformed into "copulating organs." The 
anal opening is found on the ventral surface in the midline of the telson. 


When two parts of an organism develop alike as to structure, for 
example the femur in the thigh and the humerus in the upper arm, we 
call such bones or parts homologues ( ). 

And when two parts function similarly, regardless of whether they 
are alike structurally, we call such organs or parts analogues ( ). 

While if any organ or part of an organ changes, due to a change of 
environment so as to better or benefit an organism, we call such change 
an adaptation. In the crayfish there is what is called a serial homology. 

This type of "homology" is characteristic of the group of the higher 
Crustacea known as the sub-class Malacostraca ( ), 

and this group well illustrates how a single plan of structure may run 
through a series of forms of the utmost diversity in appearance, and how 
parts essentially alike may be adapted to the most diverse ends. 

According to Lohr the "malacostracan body, be it an amphipod 
( ), an isopod ( ), a decapod ( ), 

or what not — is composed of a series of twenty 1 segments, each of which 
is essentially of the skeletal plan shown in the diagram, except that the 
appendages of the foremost segment are typically unbranched and the 
hindmost segment (the telson) is rudimentary and bears no appendages 
at all. Some of these segments may become fused together and con- 
solidated on the dorsal side, only the appendages and ventral margins 
remaining free. This may occur at either end of the body, but it occurs 
constantly in the five front segments, these by fusion forming the head. 
The appendages of these five segments always consist of two pairs of 
antennae at the front, one pair of mandibles beside the mouth, and two 
pairs of maxillae following the mandibles." These parts and their func- 
tions will readily be understood a little later because of their likeness 
to the parts bearing the same names in the insects shortly to be studied. 
"Immediately following the maxillae are one or more pairs of maxilli- 
peds, likewise directed forward beneath the mouth to assist in the manip- 
ulation of the food. Then follow legs and swimmerettes in more or less 
variety, the terminal joints of some of the legs being modified in many 
cases into highly specialized grasping organs called pincers, or chelipeds, 
and the swimmerettes being frequently modified to serve reproductive or 

1 This is not counting a vestigial segment in the head region, that is discoverable only during 
embryonic life. 


General Biology 


gk D 

A to D. Diagram of model gastric mill which can easily be made. After W. 
E. Roth; A, Cardboard as first cut out; B, Model complete at rest; C, Model 
complete; muscles contracted; D, Median vertical section of model to show folds. 

Instructions : 

Cut out a piece of card shaped as in Fig. A. Along ab, cd, ef, hi, and mn 
cut just the surface of the card with a penknife; do the same, but on the opposite 
face of the card, along gk and lo. Then bend slightly downwards the triangular 
pieces 2, 2; turn 9, 9 under the piece 6, 5, 6 until the lower surfaces of 9, 9 are fiat 
against that of 6, 5, 6; stitch the shaded part of 9, 9 firmly by thread or fine 
wire to 6, 5, 6; then bend the unshaded part of 9, 9 till at right angles to the 
shaded part, using lo as hinge-line. These projecting pieces of 9, 9 then represent 
the lateral teeth. 

Next bend the piece 1, 3, 4 upon the hinge-line gk, until the shaded portion is 
flat upon the surface of 4, where it must be securely stitched; this done bend back 
1, 3 on hinge-line cf until 3 is at right angles to 4. The projecting end of 4 made 
prominent by these folds represents the central tooth. The piece 1 must now 
be bent gently downwards upon 3, using cd as hinge-line, and 4 must be bent 
sharply on 5, using mn as hinge-line. Lastly, perforate the corner of 6, 6 and 
of 2, 2, and by a single wire (to allow a certain amount of rotation) unite right 
hand 2 to right hand 6, and left hand 2 to left hand 6, in each case 2 being 
outside 6. To do this 6, 5, 6 must be bent like a bow, its right and left arms 
being thrust downwards and inwards. The model will then be as in Fig. B. 

If now the pieces 8, 8 and 7, 7, which represent the anterior and posterior 
gastric muscles, are pulled so as to represent the effect of a muscular contraction 
the three teeth come sharply together, but are separated again and the whole 
model brought back to its original condition by the elasticity of the cardboard. 
Of course in the actual stomach of the crayfish the gaps between the ossicles are 
filled in with thin, flexible chitin. By carefully adjusting the size and direction 
of the 3 teeth in the model and further by hardening them with sealing-wax or 
similar material, they may be made to grind bread, etc., into small fragments. 
A sectional view is shown in Fig. D. 

E. Stomach or "gastric mill" of the crayfish cut through the middle. c, 
cardiac regions of stomach; d.l., duct from the liver; g, gastrolith, or calcareous 
disk secreted by the walls of the stomach; i, intestine; l.t., lateral teeth of grind- 
ing apparatus; m.t., median tooth; oe, oesophagus; py, pyloric region; v K valve be- 
tween cardiac and pyloric regions of stomach. (After Hatschek and Cori.) 

The Arthropoda 319 

respiratory functions. The eight segments following the head consti- 
tute the thorax and the seven last segments (counting the rudimentary 
twentieth segment), the abdomen. 

"Crustaceans being primitively free-swimming aquatic animals, it is 
their swimming appendages that are least altered by adaptations. The 
legs are the stoutest of the appendages, and these offer but one branch 
arising from the basal piece, and that composed of a reduced number of 
highly differentiated segments. A comparison of a leg with the last 
maxilliped in the crayfish will show which appendage has been lost and 
which preserved and specialized. The best clues to interpretation of 
homologies in any appendage are likely to be found in other adjacent 
appendages, which, because of proximity, have been subject to somewhat 
similar influences." 


Crayfish live chiefly on living snails, tadpoles, young insects, and 
the like, but sometimes eat one another, and may also devour decaying 
organic matter. They feed at night, being most active at dusk and day- 
break. The maxillipeds and maxillae hold the food while it is being 
crushed into small pieces by the mandibles. The food particles pass 
down the oesophagus into the anterior, cardiac chamber of the stomach, 
where they are ground up by a number of chitinous ossicles forming the 
gastric mill (Fig. 205). When fine enough, the food passes through a 
sieve-like strainer or hair-like setae into the pyloric chamber of the stom- 
ach ; here it is mixed with a secretion from the digestive glands brought 
in by the hepatic ducts. The dissolved food is absorbed by the walls of 
the intestine. Undigested particles pass on into the posterior end of the 
intestine, where they are gathered together into faeces, and egested 
through the anus. 


As in the frog, the nourishing fluid, the blood, is pumped by 
the heart (Figs. 206, 207) through the arterial system to the different 
parts of the body. The blood of crayfish is generally colorless or pinkish 
in hue, but on standing, especially if exposed to air, it assumes a bluish 
color. This is due to haemocyanin, a respiratory protein, which has 
copper in its nucleus. 

Before moulting, the blood of the crayfish is pink in color, due to a 
dissolved pigment, tetronerythrin, a lipochrome, which is probably de- 
posited in the new chitinous covering, since it is present in less quantity 
in the blood after the complete formation of the new exoskeleton. 

The blood of the crayfish transports food, gases, and wastes, quite 
as does the blood of the frog. 

The crayfish does not possess a true venous system and the heart. 
has only a single large cavity. The open spaces in the animal's body 
through which the blood is returned to the heart are called sinuses. 


General Biology 

The heart itself, lying close to the dorsal surface of the midline, 
constricts when filled with blood. This constriction sends blood pos- 
teriorly through the dorsal abdominal artery, which lies on the dorsal 
surface of the intestinal tract, and through a short branch known as 
the sternal artery, which passes downward crossing the intestinal tract. 
The blood is also thus sent to the ventral thoracic artery anteriorly, and 
posteriorly to the ventral part of the body through the abdominal artery. 

The arteries passing out of the 
anterior portion of the heart are the 
ophthalmic, supplying the stomach 
oesophagus, and head, and the two 
antennary, carrying blood to the 
stomach, antennae, excretory or- 
gans, and the various other tissues 
of the head. The two hepatic 
arteries lead to the digestive glands. 

When the blood is forced 
through the arterial system, the 
heart naturally collapses, and the 
blood which has been sent out forces 
the blood which is then present in 
the arteries to be sent forward 
through the glands. The function 
of these glands is similar to that of 
the lungs in the higher forms of animals, aerating the blood and sending 
it to the large open place around the heart known as the pericardial 
sinus. The heart itself has two openings on both dorsal and ventral 
surfaces, and one on each side. The heart muscles, after constriction, 
again expand and the blood in the pericardial sinus seeps through the 
six heart openings, filling the cavity. Each of the openings possesses 
a valve which prevents the blood from passing out, except through the 
arterial channels. 

It is interesting to note that this method is just the reverse of that 
occurring in fishes where the blood passes through the heart first 
and thence to the gills, while in the crayfish it is the returned blood that 
passes through the gills before reaching the heart. 

Unless colored matter of some kind is injected into the circulatory 
system, the student will probably have some difficulty in finding either 
heart or arteries. 

Valves are present in all the arteries at the point of connection with 
the heart, and blood passes into numerous capillaries and thence into the 
open spaces between the tissues, until it reaches the external sinuses, 
from which it enters the gill channels, to pass into the gill filaments 
where oxygen from the water in the branchial chambers is exchanged for 

Astacus fluviatilis. The heart A, From 
above; B, from below; C, from the left side; 
a.a., Antennary artery; a.c, alae cordis, or 
fibrous bands connecting the heart with the 
walls of the pericardial sinus; b, bulbous dila- 
tation at the origin of the sternal artery; /i.e., 
hepatic artery; I. a.; lateral valvular aper- 
tures; o. a., ophthalmic artery; s.a.a., superior 
abdominal artery; st.a., sternal artery in B 
cut off close to its origin. (From Dougherty 
after Huxley.) 

The Arthropod a 


the carbonic acid held in solution in the blood. From here it passes 
by way of other gill channels into the branchio-cardiac sinuses ; thence 
to the pericardial sinus into the heart. 


The crayfish, living in, and breathing through water, has branchial 
chambers, which contain gills (Fig. 204, B) instead of lungs, to form its 
respiratory system. These gills are pyramidal in shape and are thrown- 
out into many flaps or lamellae closely packed together. Each gill has a 
ventral and a dorsal vessel through which the blood from the body cavity 
passes into the gills, spreading out through tiny capillaries into the 
lamellae ( ). These capillaries are continuous with 

similar capillaries emptying into the dorsal vessel. 

Fig. 207. 

Semi-diagrammatic view of internal organs, and some limbs of right side of 
a male Crayfish. Astacus fiuviatilis. 1. Antennule. 2. Antenna. 3. Mandible. 4. 
Mouth. 5. Scale or squama of antenna, exopodite. 6. Anus. 7. Telson. 8. Opening 
of vas deferens. 9. Chela. 10. 1st walking leg 11. 2nd walking leg. 12. 3rd 
walking leg. 13. 4th walking leg. 14. 1st abdominal leg, modified. 15. 2nd 
abdominal leg, slightly modified. 16. 3rd abdominal leg. 17. 4th abdominal leg. 18. 
5th abdominal leg. 19. 6th abdominal leg, forming with telson the swimming 
paddle. 20. Oesophagus. 21. Stomach. 22. Mesenteron, mid-gut. 23. Cervical 
groove. 24. Intestine. 25. Cerebral ganglion. 26. Para-oesophageal cords. 27. 
Ventral nerve-cord. 28. Eye. 29. Heart. 30. Sternal artery. 31. Dorsal abdom- 
inal artery. 32. Ventral abdominal artery. 33. Ventral thoracic artery. 34. 
Ophthalmic artery. 35. Antennary artery. 36. Hepatic artery. 37. Testis. 38. 
Vas deferens. 39. Internal skeleton. 40. Green gland. 41. Bladder. 42. External 
opening of green gland. (From Latter after Howes.) 

The venous blood in all parts of the body other than the gills, passes 
through what is called an open sinus system, whereas in the gills them- 
selves the anastomosing arch of the arterial and venous capillaries forms 
a closed system. 

The thin-walled flaps of the gills are in contact with the water, which 
is sent through the branchial chamber by the muscles of the scaphogna- 
thite ( ), a sort of scoop consisting of the fused 

bract and exopodite of the second maxillae. This scoop bales the water 

322 General Biology 

out of the forward end of the gill chambers. The swimmerettes, being 
in constant motion, send water forward to the gill chambers. The blood 
thus comes in contact with fresh water, is aerated, and gives off its car- 
bon dioxide. The gills which are on the appendages themselves, are 
called the podobranches ( ), while those on the basal 

part of the appendix are called arthrobranches ( ), 

on account of being on the joint itself, and those which originate on 
the body-wall are the pleurobranches ( ). 


Contrasting interestingly with many of the other animals studied 
in the laboratory, the excretory organs of the crayfish are in the head 
region. They consist of two rather large, green glands (Fig. 207), just 
in front of the oesophagus, with a thin-walled dilated portion called the 
bladder, and a duct opening to the exterior through a pore at the top of 
a little elevation on the basal segment of the antenna. 


The nervous system (Fig. 208, B) is very much like that of the 
earthworm. The central nervous system is made up of a ventral chain 
of nerve ganglia, though it lies dorsal to the ventral blood vessel. The 
ventral chain possesses a ganglion for practically every segment, from 
its posterior end forward. The seventh is called the sub-oesophageal 

The brain sends nerves to the eyes, antennules, and antennae. The 
sub-oesophageal ganglion, lying in segment seven, is made up of the 
ganglia from segments three to seven fused together. These send nerves 
to the mandibles, maxillae, and first and second maxillipeds. Visceral 
nerves are also supplied from the brain, extending posteriorly to the 


Each eye (Fig. 208, A) is made up of some 2,500 little square facets. 
The long rod extending immediately behind each facet is called an 
ommatidium. It is supposed that the crayfish can thus see moving 
objects much better than it could if it had an eye similar to higher 
forms. But there being so many facets, it is assumed that the animal 
obtains what is called a mosaic image, an image made up of a great many 
separate and distinct views. However, as Latter says, "We must not 
confuse the image we think the animal obtains with the impression 
that is given it, for the human eye sees an inverted image but the im- 
pression is just the opposite." 

Although each ommatidium has a small range of vision and forms 
a stiple or mosaic image, it has been calculated that the range of adjoin- 
ing ommatidia overlaps so that a continuous picture or image is formed. 

The Arthropoda 


— <r. £ 


n. cA 

n.t. — 

Fig. 208. Ommatidium and Central Nervous 
A. An ommatidium or eye-element from 
the eye t»f the Lobster, c, cornea (cuticle) ; 
eh., corneal hypodermis, which secretes the 
cuticle; co., cone cells; cr., crystalline cone; n, 
nuclei; n.f., nerve fibres; r.d., distal or outer 
retinula cells; r.p., proximal or inner retinula 
cells; rh„ rhabdome, (After G. H. Parker.) 

B. A semi-diagrammatic view of central 
nervous system of a crayfish, ab.l, ab.6, The 
first and sixth abdominal ganglia; cer., cere- 
bral ganglion; c.oes., circumcesophageal com- 
missure; I.e., longitudinal commissures of 
ventral cord; n.ab.L, nerves to abdominal 
limbs;, nerve to antennule;, 
nerve to antenna;, nerve to cheliped; 
n.m., nerves to limbs adjoining the mouth; 
o.n., optic nerve; s.oes., subcesophageal 
ganglion; st.a., sternal artery; th.l, th.6, first 
and sixth thoracic ganglia; v.n., nerve to 
proventriculus ; v.n'., nerve to hind-gut. 
(After Borradaile.) 

Thus, three adjoining facets might view the word "Biology" in this way: 

Bio olo ogy. 
That is, facet one, would see the first three letters, facet two the 
middle three, and facet three the last three. But since the range of each 
facet overlaps that of the adjoining, the image formed is actually this : 

Bio ogy 
In other words, instead of an apposition image or mosaic, a super- 
position image or continuous picture is formed. 1 

1 Microphotographic studies have definitely demonstrated that the account here given is the 
correct one. 

324 General Biology 

It is doubtful whether the crayfish can hear. Some of the older texts 
in biology speak of an otocyst ( ), but the newer ones 

have discarded this name entirely ; for that organ, which was supposed to 
be used for hearing, has come to be considered a balancing organ by 
which the animal knows whether or not it is right side up and which, 
thereby, makes it possible for the crayfish to adjust its position and 

These little chitinous lined sacs on the basal segment of each anten- 
nule are now called statocysts ( ). There are a 

number of sensory hairs in this sac and a few grains of sand called stato- 
liths. These latter are placed there by the crayfish itself. These little 
sand grains coming in contact with the sensory hairs make it possible 
for the animal to determine its direction and position while swimming. 
The statocysts are therefore called organs of equilibrium. The statocysts 
are shed whenever the animal molts. 

We do not know whether the crayfish has a definite sense of smell 
or not. When meat juices or tiny particles of meat are so placed in 
the water that a slight current, carrying some of the meat, comes close 
to the animal's feelers, it begins working its jaws. This may, however, 
be either a sense of touch, or taste, or smell. 


As the crayfish possesses an exoskeleton, all of the muscles are 
attached to the interior of its casing. The strongest muscles are in the 
abdomen. It is by means of these that the abdomen can be bent quickly 
and easily, producing a powerful stroke in the water and shooting the 
body backward rapidly. All of the appendages are also supplied with 
muscles. The muscles are very beautifully arranged, though quite com- 
plicated and rather difficult to work out. 


Crayfish are dioecious, that is, the two sexes are separate (Fig. 209). 
The male (Cambarus) possesses tri-lobed testis (one pair lies anteriorly 
and a single lobe lies posteriorly) in which the spermatozoa arise. The 
spermatozoa pass through the vasa deferentia ( ) 

out of the paired genital openings in the last pair of thoracic legs. 

In the female there is a bi-lobed ovary in which the eggs are found. 
These, upon ripening, pass through the parent oviducts out of the genital 
openings, one of which is located in each base of the third walking leg. 
The sperm are transferred from the male to the seminal receptacle of 
the female during copulation, which takes place most frequently in the 
autumn. The seminal receptacle itself is a cavity in the fold of the 
cuticle between the fourth and the fifth pairs of walking legs. 

The eggs are usually laid in April and probably fertilized at that 
time. The female exudes a sticky substance upon the swimmerettes 
after lying upon her side for several days and cleaning and polishing 

The Arthropoda 


them very thoroughly. When the eggs are laid, they adhere to the swim- 
merettes which are moved back and forward through the water, thus 
aerating the eggs. It takes from five to eight weeks for the eggs to 

Fig. 209. 

A. Male reproductive organs of crayfish, t., Testes; vd., vas deferens on last 
walking leg. (After Huxley.) 

B. Female reproductive organs of crayfish, ov., Ovaries; ov'., fused posterior 
part; od., oviduct; vu., female aperture on the second walking leg. (After Suckow.) 

C. Spermatozoa of a crayfish. C. Whole spermatozoon from above; D, part, 
enlarged, from the side, cps., Capsule; pr., stiff processes. (After Borradaile.) 

hatch, the larvae clinging to the egg shell. In about" two days the first 
molting or ecdysis takes place. Like any animal possessing an exoskele- 
ton the crayfish finds it impossible to grow without splitting its exterior 
covering and getting a new one to take its place. 

The young stay with the mother about a month, then shift for them- 
selves. Crayfish attain an age of approximately three or four years. 
They molt at least seven times during the first summer. 


We have seen how the earthworm, if it is divided in a region pos- 
terior to the vital organs, will grow a new tail for the forepart, as well 
as a new tail-like portion on the tail itself. In the latter case, the animal 
starves to death, because there is no way of eating. 

With the flatworm Planaria, all manner of fantastic forms may be 
grown by cutting off, or splitting, or grafting. The crayfish, too, pos- 
sesses the power of regeneration to some extent, though nowhere nearly 
as much as the worms. If a leg, eye, or pincer is destroyed (Fig. 210), 
the animal grows a new appendage, though in place of an eye, it may, 
and often does, grow an appendage quite similar to one of the walking 
feet, or even a pincer, depending on how much of the original appendage 
was destroyed. 


An interesting condition of the crayfish, as well as of some of the 
other crustaceans, is the breaking off, by the animal itself, of one or more 
of its legs when caught in a position where it seems incapable of extri- 
cating itself. 

326 General Biology 

At certain points in the legs, there is a thick diaphragm with a tiny 
hole through which blood passes, and it is here that the animal breaks 
off its own leg, the tiny drop of blood there exposed coagulating almost 

immediately and thus preventing its 
bleeding to death. 

With an open blood system, 
such as the crayfish has, bleeding to 
death would be an easy matter were 
this special arrangement not made 
in the animal. A new leg, as large 

Diagram showing antenna-like organ re- ,« i , -ii j i r 

generated in place of an eye of Palaemon. aS the One lost, Will develop from 
(From Morgan, after Herbst.) ^ stump thus remaining> 

Reed declares that "autotomy is not due to a weakness at the break- 
ing point, but to a reflex action, and that it may be brought about by 
a stimulation of the thoracic ganglion as well as by a stimulation of 
the nerve of the leg itself." 

It will be seen quite readily that this power of autotomy is of con- 
siderable advantage to an animal. 


Sacculina ( ). (Fig. 212.) 

The young are active free-swimming larvae much like a young 
prawn ( ) or young crab. The adult bears abso- 

lutely no resemblance to a typical crustacean such as a crayfish or crab. 
Sacculina, after a short period of independent existence, penetrates the 
abdomen of a crab, and completes its development while living as a 
parasite in the crab. In its adult condition, it is simply a great tumor- 
like sac, bearing many delicate root-like suckers which penetrate the body 
of the crab host and absorb nutriment. Sacculina has no eyes, no mouth 
parts, no legs, or other appendages, and hardly any of the usual organs 
except reproductive organs. Degeneration here is carried very far. 

There are various other parasitic Crustacea, such as the numerous 
kinds of fish lice which live attached to the gills or other parts of fish, 
and derive their nutriment from the body of the fish. These also show 
various degrees of degeneration. With some of the fish lice the female, 
which looks like a puffed-out worm, is attached to the fish or other 
aquatic animal, while the male, which is perhaps only a tenth the size 
of the female, is permanently attached to the female, living parasitically 
on her. 


One may, with a fine-meshed net, sweep in a considerable collection 
of organisms from the surface of ponds, lakes, rivers, or ocean. There 
will be thousands of minute creatures of varying shape and size. Some 
of them are too small to be seen with the naked eye, while others are 

The Arthropoda 


easily noticed. Collections of this kind may be made from any waters 
at any time of the year, from thousands of miles out at sea, and. over 
depths of thousands of feet, to the shore line itself. The reason organ- 
isms can be found everywhere in water is due to the fact that their whole 
life is spent afloat, beginning with the egg and reaching through the 
adult stage. Living organisms of this type have been called plankton, 
and comprise protozoa, algae, diatoms, rotifera, and small Crustacea, the 
latter being especially noticeable. 

To permit a life afloat, organisms are provided with various types 
of adaptations, such as minute droplets of oil, long spines to add 
buoyancy, and gelatinous envelopes. Among the small Crustacea, spines 
and oil drops are especially abundant. Upon analysis it has been shown 
that the oil of fish is derived from these small Crustacea. The reason 
for this is easily understood when it is known that the sole food of 
several species of whale and of many fish is plankton. 


The class Malacostraca ( ) are arthropoda, 

usually of large size, with five segments in the head, eight in the thorax, 
and six in the abdomen, and a gastric mill in the stomach. These, like 
all other classes, are divided into orders. Prominent among these orders 

Fig. 211. 

A. Ascellus aquations a 1 o 2 antennae; br, brood-pouch; k, pleopoda modified 
to gills; md, mandibles; p x -p 7 , thoracic feet; pa^pa 6 , abdominal feet (pleopoda); 

XIV-XX, abdominal segments partly 

I-VI, head; VII-XIII, thoracic segment 
fused. (After Hertwig.) 

B. Oniscus asellus, a terrestrial species. 

(After Paulmier.) 

are the Decapoda ( ). The crayfish comes under this 

grouping. All members of this order have the first three pairs of thoracic 
limbs specialized as maxillipeds, and possess five pairs of thoracic walk- 
ing-legs, while all the thoracic segments are generally covered by the 
carapace. They also have stalked, compound eyes. 

The Isopoda ( ) have a body that is long and 

flat (Fig. 211, A), seven free thoracic segments, leaf-like legs, and no 
carapace. There are no gills in the thorax. 

The five anterior pairs of pleopods are modified for breathing pur- 
poses, the endopodites are thin-walled plates, and the exopodites and 
the whole first pair of pleopods serve as a gill-cover. 


General Biology 

Fig. 212. 
Development of the parasitic crustacean, 
Sacculina carcmus : A, Nauplius stage; B, 
:ypris stage; C, adult attached to its host, the 
:rab, Carcinus maenas. (After Hertwig.) 

In the terrestrial Isopoda (Fig. 
211, B) — the wood-lice — the gills are 
adapted for breathing damp air. In 
these, the first and second-gill-covers 
have air-tubes within them. These 
function like the tracheae of insects 
and are, therefore, physiologically, 
but not morphologically, compara- 
ble to tracheae. 

The many different species of 
Isopoda (except the wood-lice) are 
aquatic. There are many which are parasitic, feeding on both dead and 
living fish, and fish in turn feed on them. 

A very remarkable finding in the parasite Cymothoidae ( ), 

by Buller, is that the same individual can be developed first as a male 
and then as a female. 

Cryptoniscus ( ) is a more or less shapeless 

sac which attaches itself to the stalk of Sacculina (Fig. 212), and after 
the host (which is itself a parasite) is killed, the new parasite uses the 
"roots" of Sacculina to draw forth its own nourishment. 

The Entoniscidae ( ), which are parasitic, are 

usually hermaphrodite, although there are small males, called "com- 
plemental males," attached to the larger female. 



IT is well first to note that insects (often wrongly called Hexapoda, 
on account of their having three pairs of legs), are winged, six-legged 
arthropods (Pterygogenea) ( ) (Fig. 213). The 

body is divided into three distinct regions — the head, the thorax, and 
the abdomen. The head has the following appendages : a single pair of 
antennae ( ) ; usually two compound eyes ; three 

simple eyes called ocelli ( ) ; and four different 

kinds of mouth-parts. These mouth-parts consist of a labrum (single, 
and not one of the series of metameric appendages), mandibles, maxillae, 
and labium; these last three being paired. 

The thorax is composed of three segments — prothorax, mesothorax, 
and metathorax. Each segment is protected by four exoskeleton plates 
— a dorsal tergum, a ventral sternum, and two lateral pleura, There is a 
pair of walking legs on each thoracic metamere, while the last two 
usually also have a pair of wings attached. 

The abdomen usually consists of eleven segments, on which there 
are no appendages except accessory reproductive organs and sometimes 
a sting at the posterior end. 

In general there are two types of mouth-parts. These may vary 
considerably. Grasshoppers and beetles have biting mouths, while the 
true bugs have mouths arranged for sucking, and some insects, such as 
the bee, have specialized mouth-parts which may be used for either 
biting or sucking. 

The walking legs have five parts : a proximal coxa ( ), 

often fixed immovably to the sternum to which it is attached; a short 
trochanter ( ) ; a long femur ; a slender tibia ; and a 

jointed tarsus, usually provided with little hooks or pads at its free ends. 
As insects have varying modes of life, such as swimming, flying, digging, 
and leaping, the legs of each type of insect are adapted to the particular 
functions required. 

It is from the last two thoracic segments that the wings arise. The 
wings are of two types : Broad ones, such as the butterfly possesses, 
used for sailing; and smaller ones like those on flies, which can be moved 
quickly to cause a rapid movement of the animal. There may be scales 
or hairs on the wings. Likewise, wings may be thick or thin, light or 
heavy, and vary in many other ways. The so-called "veins" in insect 
wings are not veins at all, but thickenings supporting the wings. 

As insects are complex organisms, all the interior structures nor- 

330 General Biology 

mally found in any animal, are also 
found in them, though these may vary 
considerably as to shape and size. For 
example, those insects, which feed on 
vegetation, have longer digestive tracts 
than do those feeding on animal 

The parts of the digestive system 
(Fig. 214, E) are: The mouth or 
buccal cavity; a slender oesophagus, 
dilated to form a thin-walled crop; a 
muscular gizzard or proventriculus ; a 
glandular stomach, or ventriculus, 
from which little pouches, or caeca, 
branch out ; and a long slender intes- 
tine. At the junction of the stomach 
and intestine, the slender Malpighian 
tubules discharge their excretions into 
the alimentary canal. 

As distinguished from the higher 
forms of life no air-breathing insects 
have lungs. They receive their oxygen 
through a network of tubes, called 
tracheae, which open through little 
spiracles ( ) along 

the sides of abdomen and thorax (Fig. 

If, therefore, one wished to chloro- 
form or drown an insect, it could not 

be done by covering the head or placing the head under water. The 

abdomen and thorax would have to be covered with the anaesthetic or 

the water. 

white banded 

_ Based, band 
fiasal end of segment 
Apical end <f segment 

S tk tarsaljood- 

Fig. 213. 

I. External anatomy of Caloptenus and spretus, the head and thorax disjointed; 
up, Uropatagium; f, furcula; c, cercus. (Drawn by J. S. Kingsley.) 

II. An adult mosquito much enlarged, with all the parts that are used in classi- 
fication named. (Smith, N. J. Experiment Station, Bulletin 171, 1904.) 

III. Side view of Locust with the Thorax separate from the head and abdomen 
divided into three segments. (I, III, from Packard's "Zoology," by permission of 
Henry Holt & Co.) 

Insects at Large 


If the insect flies a great deal, these tracheae are expanded into 
air sacs, which adds to the lightness of its body. 

However, insects which live in water, have tracheal or blood gills, 
or both, or at least some specialized adaptation by which oxygen may 
be used. 


Fig. 214. 

A.-D. Successive stages in the concentration of the central nervous system of 
Diptera. A, Chironomus; B, Empis ; C, Tabanus; D, Sarcophaga. (After Brandt.) 

E. Internal anatomy of Calopte'nus femur-rubrum: at, Antenna and nerve 
leading to it from the "brain" or supra-esophageal ganglion (sp); oc, ocelli, 
anterior and vertical ones, with ocellar nerves leading to them from the "brain;" 
oe, oesophagus; m, mouth; lb, labium or under lip; if, infra-esophageal ganglion, 
sending three pairs of nerves to the mandibles, maxillae, and labium respectively 
(not clearly shown in the engraving) ; sm, sympathetic or vagus nerve, starting 
from a ganglion resting above the oesophagus, and connecting with another ganglion 
(sg) near the hinder end of the crop; sal, salivary glands (the termination of 
the salivary duct not clearly shown by the engraver) ; nv, nervous cord and gan- 
glia; ov, ovary; ur, urinary tubes (cut off, leaving the stumps); ovt, oviduct; 
sb, sebaceous gland; be, bursa copulatrix; ovt' , site of opening of the oviduct (the 
left oviduct cut away); 1-10, abdominal segments. All other organs labeled in 
full. (Drawn from his original dissections by Mr. Edward Burgess.) (From 
Packard's "Zoology," Henry Holt & Co., Publishers.) 

A peculiar feature of all animals possessing an exoskeleton is that 
as soon as the inside of such skeleton grows but slightly, it becomes 
too large for its skeletal-jacket, so that it must split and a new one must 
form. This is called ecdysis ( ), or molt (Fig. 227), 

and the periods between molts are called instars. 

It will be remembered that we spoke of a double-life in the frog, 
not only as applied to its living in water and on land, but as to its begin- 
ning life looking very much different from what it does as an adult. Prac- 
tically all insects go through a metamorphosis ( ) 
of some sort, and this is much more complicated than the change under- 
gone by the frog. 


General Biology 

When insects hatch from eggs (Fig. 241, I, II), and are unlike their 
parent-forms, they are said to be heterometabolous ( ). 

Such insects hatch as nymphs ( ), a wingless form 

gradually growing larger and larger wings after each ecdysis until the 
adult form is reached. Insects are holometabolous ( ) 

if there is a complete metamorphosis, such as being born a worm-like 
larva ( ), which takes food for a short time and then 





A. Respiratory system of worker honey-bee as seen from above, one anterior 
pair of abdominal sacs removed and transverse ventral commissures of abdomen 
not shown. / sp, III sp, VII sp, spiracles; HtTraSc, Tra Sc, 1, 2, 4, 7, 8, 10, 
tracheal sacs; Tra, tracheae. (From Snodgrass, Tech. Series 18, Bur. Ent., U. S. 
Dep't of Agric.) 

B. A portion of the tracheal tissue of a cockroach, highly magnified. Only 
parts of the tubes are in focus. 

cu., Cuticular lining with spiral thickening; nu., nuclei of the protoplasmic 
layer; ppm., protoplasmic layer continuous with the epidermis ("hypodermis") of 
the surface of the body. (After Borradaile.) 

goes into a resting or pupal stage during which no food is taken, and 
during which time it loses all its larval structures, finally developing into 
a complete adult insect, known then as an imago' ( ). 

In those cases where there is no metamorphosis, the animals are 
said to be ametabolous ( ). 



WE have seen from our study of the crayfish that it was an arthro- 
pod— 1 that is, had hollow jointed feet, and that the phylum 
arthropoda is often divided for convenience into branchiata — 
(gill-breathing) and tracheata (breathing by air tubes). 

The two tracheata most commonly studied in the laboratory are the 
bee and the grasshopper in this country, and the cockroach in England. 
Each of these organisms well represents the group to which it belongs. 
The bee is the more highly specialized, and many books have been writ- 
ten about this interesting animal; in fact, so much so that the subject- 
matter covering it is almost inexhaustible. The grasshopper, however, 
because it is considerably larger than the bee, is preferred by many 

The study of this animal is representative of the greater part of the 
animal kingdom, for this is an insect, and there are more different kinds 
of insects than there are of all other animals put together. 


Some of our most important garden pests are insects, and it has 
been estimated by competent authorities, that one-tenth of all farm 
products are destroyed by such pests. Now, there are very few of us 
who would not object to being obliged to pay one-tenth of all we earned 
to anyone for the privilege of working. Still, how low our average in- 
telligence is, may be noted from the fact, that while a loss of one-tenth 
of all our food is constant, year in and year out, the average farmer 
would object very strenuously to paying out even one-tenth of the tenth 
he loses to pay the salary of a group of trained men to prevent this loss 
from occurring. And this is true, even though he would thus be in- 
creasing his income to a considerable extent. 

Let us illustrate by actual figures. The average farmer, let us say, 
has an income from all his crops (and this income, of course, includes 
his living expenses, as he raises the greater portion of his food) at the 
lowest estimate, of about $2,000 each year. He should have, if the insect 
pest were controlled, $2,200. Yet, if he were asked to contribute $20 
each year to such control he would rebel. But as each and every one of 
us must live on what the farmer produces, we must pay $2,200 for $2,000 
worth of food. That is, we must pay $100 a year extra for every thou- 
sand dollars we spend for food. 

Let us consider the item of clothes. These may be of cotton, wool, 
or silk. Cotton and wool are farm products, and so also is silk. The 
silk grower also must have this extra $100 to pay his own expenses 


General Biology 

in purchasing- food for himself and family. In the silk industry Pebrine 
— a very serious silk-worm disease — reduces the annual production of 
silk to the extent of thousands of yards and, thereby, raises silk prices. 

To make this clear, suppose a man is employed for a certain num- 
ber of days each week and a certain number of weeks in the year, and 
is paid $5 a day for such work. It follows that his employer must re- 
ceive enough money, when selling the product produced, to pay the 
worker $5 each day, plus a proportionate amount of the rent, taxes, 
bookkeeping, salesmen's salaries, and traveling expenses, as well as 
allowing interest on his investment. That is, what the worker gets $5 
for, will cost the ultimate user at least $10, for, it is just as difficult 
to sell and to deliver goods as it is to make them. But now suppose 
a storm comes up and destroys the plant, and the workman still works, 

Fig. 216. Head and Foot of Fly. 
The Foot shows hooks, hairs and pads. (Head after Herms.) 

receiving $5 each day, the traveling salesman still works, the book- 
keeper, stenographer, foreman, engineer, fireman, night watchman, are 
still all kept on the job, and receive their stated pay, but the work 
is all put into clearing away the debris and in rebuilding. It follows 
that all of this expense of keeping these men employed must be added 
to the cost of the article. This loss may be spread over a great many 
years, it is true, only a cent or two being added to the selling price of 
the article, but it must nevertheless be paid. 

Now, suppose for a moment, that such a fire takes place regularly 
every year, and that, therefore, one must work one-tenth of the entire 
year without producing anything. This is equivalent to taking the 
workman's salary away for this tenth of the year though still obliging 
him to do the work. 

Here is a parallel to the financial loss caused by insect pests alone, 
to each of us. For this is our loss. We must work an extra five weeks 
each year to pay for the fact that men at large rank so low in the intel- 

The Grasshopper 335 

lectual scale that they refuse to pay out $10 a year for each $1,000 they 
receive to prevent tremendous food and clothing losses. 

But this mere working of about five weeks each year for nothing 
is of little importance compared to the millions of lives lost each year 
by the working out of the self-same principle that makes men think 
only of the dollar they receive to-day, rather than of the ten-times-that- 
amount they may have to-morrow, if they will but lay the foundations 

Every worker who dies of a disease which could have been pre- 
vented, causes each and every one of us to do a portion of his wOrk. 
This means that we must actually pay the expenses of keeping up such 
a one's family without anything being contributed on their part. 

There is thus an underlying unity among all human beings, in that, 
whether we will or not, we are our brother's keeper. 

This is again well illustrated by taking into consideration the fact 
that your own home and property may be as clean as it is possible to 
keep it, but your neighbor's is not. The flies which breed in his manure 
pile, or in his garbage heap, will come into your home and deposit the 
neighbor's filth on your food. That this deposit is no mere trifle is 
shown by an enlarged sketch of the fly's foot and proboscis (Fig. 216). 


The hard exoskeleton has already been mentioned, as well as the seg- 
mentation of the grasshopper's body. The segments in this animal are 
unlike those of the earthworm in not being all alike. 

There are a head, a thorax, and an abdomen, to which various jointed 
appendages are attached, a pair to each segment, where any appendages 
are found. 

The three pairs of legs formerly gave insects the name of Hexapoda. 
Two pairs of wings are usually found upon the dorsal side of the second 
and third segments of the thorax, while the tiny outer openings of the 
tracheae — known as breathing pores, spiracles, or stigmata — are arranged 
in pairs on each side of two thoracic segments and on all the abdominal 
segments except the last two or three. 

Grasshoppers, as well as crickets and cockroaches, are members of 
the order Orthoptera ( ). All of this group have 

mouth-parts (Fig. 217), or jaws, formed for biting and gnawing, as well 
as two pairs of straight wings, the first pair thickened, the second pair 
thin, and, when at rest, folded like a fan under the first pair. 

A pair of jointed antennae, or feelers, extend forward from the head, 
while a pair of large compound eyes, located on the dorsal epicranium, 
and three ocelli, or simple eyes, are readily observed. The mouth-parts 
consist of the- labrum, or upper lips, being hinged to the clypeus 
( ), a pair of heavy, strong mandibles, and a first 

pair of maxillae, with feelers or palps ( ) at the sides ; 

while the second pair of maxillae are fused together to form the lower 


General Biology 

lip, called the labium, and are attached to crescent-shaped genae 
( ). The cheeks are called genae ( ), 

while narrow postgenae are back of these. 

The maxillae are the accessory jaws, and are composed of three 
regions, the lacinia or maxillae proper, the gulea ( ), 

Three ocelli or simple eyes 

Compound eyes 
Clypeus (c). 


Palpifer or palpus bearer 

labial palpi 

Fig. 217. 

A. and B. Skull of grasshopper; C. Melanoplus differentialis. a, Antennae, 
c, clypeus; e, compound eye; /, front; g, gena; /, labrum; Ip, labial palpus; m, 
mandible; mp, maxillary palpus; o, ocelli; oc, occiput; pg, post-gena; v, vertex. 
(After Folsom.) 

C. Head and Mouth-parts of an insect. (After Tenney.) 

the middle spoon-shaped part, and the maxillary palpus, a special sense 
organ. This palpus is in turn composed of various segments, the broad 
basal piece being called the stipes ( ) which joins 

in turn with a smaller cardo ( ). 

The lower lip or labium is composed of two broad terminal flaps 
called the ligula ( ). The mentum ( ) 

is the basal portion, while the small immovable submentum lies between 
the mentum and the gula. 


The right wing of a male mosquito, Anopheles maculipennis. A, anal area; 
1st A, anal nervure; C, costa; Cu, cubitus; H, humeral cross-nervure; /, cross- 
nervure between R and i? 4 + 5 ; J, cross-nervure between radial and medial sys- 
tems; K, cross-nervure between medial and cubital systems; M, media; O, cross- 
nervure between R x and R n ; R, radius; Sc, sub-costa. (From Sedgwick's Zoology, 
after Nuttal and Shipley.) 

The thorax is divided into a prothorax, mesothorax and metathorax, 

easily distinguished by the three pairs of legs, one pair of which is 
attached to each of the three thoracic divisions. The prothorax consti- 

The Grasshopper 


tutes a collar which is drawn out into a shield above. The wings, as 
already stated, are attached to the dorsal side of the mesothorax and 

The wings are divided by veins or nervures (Fig. 218) into so-called 
cells. Although these veins, or nervures, vary considerably in different 
species, they are quite constant in members of the same species and so 
are often used as a basis of classification. 

The principal longitudinal veins are the costa ( ), 

subcosta, radius, media, cubitus ( ), and anal. 

There are also cross veins. Any variations are the result of either 
additional and lessened number of those just mentioned. In beetles the 

fore-wings are sheath-like and called elytra ( 

The fore-wings of grasshoppers and all members 

grouping are leathery and called tegmina ( 

The abdomen consists of eleven segments, the 
clearly defined than the others. 

The entire exoskeleton is divided by sutures ( 
into distinct pieces, the sclerites ( 
of these sclerites may fuse. 


of the Orthoptera 


posterior one less 


), though several 

Fig. 219. Ear of Locust (Caloptenus italicus) as seen from the inner side. 

T, tympanum; TR, its border; o, it, two bone-like processes; bi, pear-shaped 
vesicle; n, auditory nerve; ga, terminal ganglion; st, stigma, or spiracle; m, open- 
ing muscle, and m 1 closing muscle of same; M, tensor muscle of tympanic mem- 
brane. (After Graber.) 

The sclerites (Fig. 204, A) on the dorsal surface are called tergites 
( ). These are often fused together in various 

insects. The sclerites on the ventral surface are known as sternites 
( ), while the side walls connecting dorsal and 

ventral sclerites are called pleurites ( ). 

33$ General Biology 

The entire dorsal portion is spoken of as the tergum or notum 
( ) ; while the entire ventral wall is called the 

sternum; and the lateral wall, the pleuron. 

The last tergum is sometimes called the suranal ( ) 

plate, while the last sternite forms the subgenital plate. Below the level 
of the eleventh tergite, on each side, there is a triangular podical plate 
( ), and just above each podical plate and projecting 

backward from the hind margin of the tenth tergite there is a small 
copulatory organ, the cercus. In the female this is extremely small. 

The auditory ( ) organs (Fig. 219) lie on the 

first abdominal segment. This segment is larger than the others though 
it does not form a complete ring on account of the hind legs being 
inserted in it. This auditory organ is merely an oval spot of thin skin 
stretched across a small cavity and connected with a nerve. This is 
the ear or auditory apparatus. 

The posterior portion of a female's abdomen is more tapering than 
that of the male and is furnished with four blunt spines (six including 
the inner guide), to form the egg-laying organ, the ovipositor. The 
tip of the abdomen in the male is turned upward. 

The first two pairs of legs on the grasshopper are walking legs 
while the third pair is used for jumping. 

Using one of the first walking legs for detailed study, we find five 
separate divisions (compare Figs. 203 and 213) into which it can easily 
be separated, namely, the coxa ( ), the shortest joint 

in close proximity to the body; the trochanter ( ), 

the next succeeding small joint almost entirely fused with the coxa in 
the grasshopper; the femur ( ), a long stout section; 

the tibia ( ) following this, also long and quite 

narrow ; and finally the most distal portion, the foot, called the tarsus 
( ), which is composed of four joints. 

There are spines on the leg and claws [also called ungues 
( )] on the foot; while a suction disc, the pulvillus 

( ), lies between the claws. The longer jumping 

leg has the same five divisions just mentioned, but the trochanter is fused 
with the femur, forming a small knob on the inside of the leg. 


This consists, as in all the other animals studied, of the alimentary 
canal and the collateral or accessory organs, the salivary glands, and 
the gastric caeca. 

The alimentary canal itself is a long tube extending throughout the 
entire body. The mouth is the first division and is guarded on each side 
by laterally moving mandibles. Between these mandibles and arising 
from the inner side of the labium, is the short tongue-like organ known 

The Grasshopper 339 

as the hypopharynx, at the base of which a tube opens from the several 
salivary glands. The epipharynx is the organ of taste, and is located on 
the slightly convex surface of the inner side of the labium. 

The continuation of the mouth leads into the short curved oesopha- 
gus which in turn leads to the large ingluvies ( ) or 
crop. Here are seen various rows of spine-like teeth. The proventric- 
ulus, or gizzard ( ), follows. This is a very small 
organ also furnished with spines ; it empties into the large, thin-walled 
ventriculus or stomach. Six tubular gastric caeca, or blind sacs, are 
attached to the anterior end of the stomach. Posterior to the stomach 
the alimentary canal forms the intestine which is divided into three 
portions: the ileum ( ), rather slender, with 
longitudinal ridges on the inside (the infolding ridges increase the 
absorbing surface) ; the colon, smaller than the ileum and possessing a 
smooth lining; and the rectum, which has six longitudinal rectal glands 
of unknown function. 

The food of the red-legged locust, which feeds quite freely by day 
(unlike the crickets and katydids which are more active at night), con- 
sists of grass and little drops of dew. The pads at the tips of the legs, 
and the claws, enable the animal to climb stalks of all kinds very readily. 
This eating of dew rather than drinking at pools of water, has given us 
the idea that there is something about standing-water that is fatal to 
the grasshopper. That this idea is correct is evidenced by the fact that 
grasshoppers kept in captivity must be sprinkled with drops of water or 
they usually perish. 

As food is taken into the mouth, the salivary glands pour their 
secretions forth to assist in preparing it for reception in the crop to 
which it passes through the oesophagus. Here it is mixed with a 
molasses-colored digestive fluid. It then passes on to be ground up 
still further by the spinous processes in the muscular gizzard. The 
various gastric caeca, each of which has an anterior and a posterior 
pocket, increase the stomach space. 

Once the food has passed through the stage just mentioned, it be- 
comes part of the blood of the grasshopper. This it does by being 
absorbed through the walls of the alimentary tract. 


The grasshopper has a long tubular heart (Fig. 214, E) lying along 
the dorsal surface just beneath the body wall. From the heart there are 
arteries and sinuses connecting the various parts of the body. Due to its 
position the heart is often called the dorsal vessel. 

Anteriorly the heart is prolonged into a tube leading to the head and 
is partially divided by valves into eight chambers. The position of the 
heart-valves allows blood to flow headward only. 

340 General Biology 

The propulsion of the muscular heart sends the blood forward 
through various sinuses so that every part of the body is nourished 
by it. It then returns by a closed tube, the ventral sinus, to the peri- 
cardial sinus or chamber, and enters the heart through several pairs of 
lateral ostia ( ). If more food has been absorbed 

than can be used, it is stored up as fat in the fat bodies on either side 
of the heart. 


The blood of all insects (Fig. 220) contains a respiratory protein, 
hemocyanin, similar to that of the crayfish. In some few species (blood- 
worms=midge larvae, Chironomidae) hemoglobin is also found. Since 
the hemocyanin is capable of absorbing oxygen and carbon dioxide, it 
is probable that in the insects this respiratory protein aids the tracheae 
in distributing oxygen and collecting C0 2 . The tracheae are kept open 
and extended by a spiral thickening of chitinous lining and extend to all 
parts of the body even including the legs and wings (Fig. 215, B). 

This is, no doubt, one of the reasons why the circulatory system is 

so poorly developed, for, unlike the 
higher forms of animal life where 
the circulatory and respiratory sys- 
tems are dependent upon each other, 
Fig. 220. Blood Corpuscles of the Grasshop- the systems in the insects are sepa- 

per, Stenobothrus. . , , . , . , , 

rate and distinct, so that every part 

a-f, corpuscles covered with fat-globules, r ,■• U^A * , ~ U~ ^..^^1:^^I l-t-U 

g., corpuscle after treatment with glycerine, Ot the body Can be Supplied With 

showing nucleus. (After Graber.) oxygen at any time, regardless of 

what may happen to another part. The disadvantage of such a method 
consists in the necessity of having both a respiratory system and a 
circulatory system in every part of the body instead of having all 
respiratory work done in one place. The air sacs with which the 
tracheae are connected are of value in making the animal light for flying 
and jumping purposes. The grasshopper can beat any professional 
human jumper by the distance it covers in a single leap when compara- 
tive size is considered. 

If one notices a grasshopper when it breathes rapidly, it will be seen 
that the abdomen lengthens and shortens, thus forcing air in and out of 
the spiracles on the thorax and abdomen. 


Like all animals, the grasshopper needs oxygen to carry on its meta- 
bolic processes, and, like all animals, it gives off carbon-dioxide as a 
waste product as well as water and a nitrogen-containing-substance 
called urea (if in solution) or uric acid (if crystalline). It is interesting 
to note that those grasshoppers, which live in dry places, excrete the 

The Grasshopper 


crystalline product while those, which live in damp places, excrete the 
soluble form. 1 

The excretory products leave the body through the urinary or 
Malpighian tubules which empty into the intestine just posterior to the 
stomach, thus causing both the excreted and egested material to leave 
the body in the same way. These tubules ramify throughout the body 
in the animal and are very conspicuous when the body is opened. 


The nervous system resembles that studied in the crayfish. A 
series of ganglia lie along the ventral nerve cord which splits at the 

Fig. 222. 

Reproductive system of the Queen honey 
bee. a, accessory sac of vagina; b, bulb of 
stinging apparatus ; c, _ colleterial, or cement 
gland ; o, ovary; od, oviduct; p, poison glands; 
pr, poison reservoir; r, receptaculum seminis; 
re, rectum; v, vagina. (After Leuckart.) 

Fig. 221. 

A, diagram to illustrate the action of 
wing-muscles of an insect. 

B, diagram of wing-muscles. a, alimen- 
tary canal; en, muscle for contracting thorax, 
to depress wings; d, depressor of wing; e, 
elevator of wing; ex., expandor of thorax to 
elevate wing; id, indirect depressor; ie, in- 
direct elevator; /, leg muscle; p, pivot or ful- 
crum; s, sternum; t, tergum; wg, wing. 
(After Grabers.) 

oesophagus, one half passing dorsad on each side of that organ to 
unite again on the dorsal surface to form the supraoesophageal ganglion 
or brain. The ganglion below the oesophagus which branches to permit 
the passing around to form the brain is called the suboesophageal 
ganglion. It is from the brain that nerves go forward to supply the 
special sense organs, such as the eyes, antennae, and labrum, while the 
mandibles and maxillae are supplied from the suboesophageal ganglion. 
Nerves are given off from the thoracic and abdominal ganglia to all 
parts of the respective segments. The interesting thing about insects 
is that these nerve centers seem to be as independent as are the separate 

x Doubt has been thrown on former investigations by recent work, so it is well not to assume 
that our opinions in regard to the work of the Malpighian tubules or of the formation of urea 
are final. 


General Biology 

respiratory tracheae in that the head may be removed while the other 
parts of the body continue their work almost as well as before. 

In addition to the Central Nervous System and the regular Pe- 
ripheral Nervous System consisting of the segmental nerve filaments, 
there is also a Sympathetic System, divided into two parts, one lying 
dorsal to the alimentary tract and controlling the digestive processes 
while the other lies ventral to the alimentary tract and controls the 
spiracle muscles. 


We have already seen that there are simple and compound eyes in 
an insect. An ocellus, or simple eye (Fig. 223), is made up of a lens, 
vitreous body, retina, and nerve, quite like that of the frog, except that 
the insect's eye is definitely fixed. It cannot accommodate itself to dis- 
tance. Its power of vision is, therefore, 
more limited, and because the lens is quite 
convex and only able to focus at one dis- 
tance, it is assumed that insects must be 
very near-sighted. 

The surface of the compound eye is 
made up of numerous facets each at the end 
of a single eye-element called an omma- 
tidium (Fig. 208, A), which, as already de- 
scribed for the crayfish, is, in a way, a sepa- 
rate and distinct eye. 

Recent investigations of the structure 
of ommatidia show that these are more or 
less conical, the narrow end at the base 
being connected with the nerve fiber. It 
is assumed that the field of vision of each 
ommatidium overlaps slightly that of the 
adjoining ones. This assumption is sup- 
ported by the fact that the lens of each ommatidium is convex, so that 
not only rays in direct line but lateral rays are refracted on the nerve 
fiber. In this way a superposition image is formed, not the apposition 
image, or mosaic, described by older authors. 

Recent work on the ocelli and compound eyes indicates both of these 
structures work together to increase recognition of movement. This is 
due to the fact that the rays of light reach the ocelli and compound 
eyes at different angles. There is additional evidence that the ocelli 
are used to distinguish light from darkness. Certain night-flying bees 
and dragonflies have greatly enlarged ocelli. Because of the fixed focus 
of the ocelli and the great convexity of the lens, the object to be seen 
must be very near. 

Whether insects perceive color as such is a question of much dis- 

Fig. 223. 


Median ocellus of honey 
(Longitudinal section). h, hypo- 
dermis; /, lens; n, nerve; p, iris 
pigment; r, retinal cells; v, vitreous 
body. (After Redikorzew.) 

The Grasshopper 


pute. Very little direct evidence is available; most of it is circum- 
stantial. Many authors and experimenters hold that insects recognize 
colors only as shades of gray, much as a color-blind person does. On 
the other hand, not a single experiment to prove color vision has demon- 
strated such a fact. It is not a necessary correlation that because 
flowers are colored, insects see colors. Half of the good pollinators are 
night fliers. 


The sense of touch is probably very highly developed in most in- 
sects as there are sensory tactile hairs over the entire body, as well as 
antennae, palpi, and cerci which are also special tactile organs. 

Fig. 224. 

A. The common cricket, Gryllus Pennsylvanicus, female. Line indicates 
natural size. 

B. Oblong leaf-winged Katydid, Amblycorypha oblongifolia, female. (From 
Kellogg's "American Insects," by permission of Henry Holt & Co.) 


The sense of taste is located in the sensory hairs; in the micro- 
scopic elevations borne upon the tongue or hypopharynx, on the epi- 
pharynx (which lies on the roof of the pharynx, and is something like 
the palate in higher animals), and on the maxillary and labial palpi. 
From the experiments so< far performed it seems insects can detect tastes 
that man cannot. 


Insects may depend upon the sense of smell to find their food more 
than upon sight, but the usual experiments to demonstrate this are far 
from satisfactory. The cutting away of antennae with the attendant 

344 General Biology 

tearing of many tiny nerves will certainly not cause any organism to 
react normally. 

Mclndoo has recently shown that the chief olfactory organs (at 
least in the honey bee) are located near, or on the base of the leg. 


As various insects produce noises of many kinds, we infer they must 
hear, though definite evidence has not been forthcoming up to this time. 
Flies and bees "buzz" by a rapid motion of the wings, while the singing 
of the male cicada is produced by a rapid vibration of a pair of mem- 
branes on the first abdominal segment, and a resounding drum-like mem- 
brane within the thorax. Many beetles form a squeaking noise by 
rubbing their wing-covers against some rasp-like portion of their body 
while grasshoppers rub their hind legs against the wing-covers and also 
rub front and hind wings together. 

Crickets and katydids (Fig. 224) have a definite scraper on the base 
of one wing-cover and a file-like apparatus on the base of the other. 
These are rubbed together causing the neighboring membrane to vibrate 
and produce the "chirp." 

As such "chirps" or calls are answered by their mates it must be 
assumed that some hearing takes place. 

The grasshoppers have a large auditory organ on each side of the 
first abdominal segment consisting of a surface membrane, or tympanum, 
stretched across a cavity, on the inside of which two tiny processes 
something like the ear-bones of the frog are found. There are also 
similar membranes on the tibia of some insects which probably serve 
as auditory organs. 

A male mosquito will vibrate its antennae when a tone is produced 
on a tuning fork of the same pitch as that made by the wings of the 
female, so that it may be that in the mosquito the antennae have some 
auditory function. 


As in all animals possessing an exoskeleton, the muscles must be 
attached on the inner surface of the skeleton (Fig. 221). Each of these 
muscles is innervated by nerves, however, just as in animals possessing 
endoskeletons and each muscle moves by a series of complicated pulley- 
like arrangements already described in the crayfish. 


Among all insects there are two sexes, the male usually being the 
smaller, more active and more brightly colored. It has been suggested 
that the reason for this is that the handsomer males are thus able to 
attract mates more often than those less handsome. Consequently the 
young born of such more handsome fathers, were also handsome, thus 

The Grasshopper 


eliminating, by natural selection, the less handsome. It has been sug- 
gested by some also that the female, who carries the eggs, by being less 
gaudy in appearance is also less conspicuous and, therefore, not so likely 
to be caught by natural enemies. 

In all female insects there are a pair of ovaries (Fig. 222) usually 
formed of many small tubes called ovarioles. From the ovaries the 
oviducts pass out into a terminal region, the vagina, which is sometimes 
also paired. This latter organ is usually formed by an invagination from 
the outer part of the body to meet the oviducts. Near the place of 
meeting of vagina and oviducts or branching off from that region there 
is a receptaculum for receiving and holding the male sperm received 
during copulation. 

Then there are accessory glands which secrete a sticky substance, or 
cement, as the eggs pass through the oviduct. These glands are known 
as colleterial or sebific ( ) glands which open in turn 

into the dorsal portion of a capacious pouch, the bursa copulatrix, 

through a duct. This bursa rests 
on, and opens directly into, the 
oviduct of the female. Grasshoppers 
have an external hard posterior re- 
gion of the body known as an ovi- 
positor (Fig. 225). 

The males possess a pair of 
testes usually formed of many small 
tubes. These tubes, in turn, connect 
with two ducts, the vasa deferentia, 
which carry the sperm to the termi- 
nal portion called an ejaculatory 
duct. The ejaculatory duct may 
have one or two openings which may 
be formed by the union of both vasa 
deferentia or by an invagination 
meeting these ducts. 
The seminal vesicles, usually paired, open from either the vasa 
deferentia or the ejaculatory duct. Here sperm are stored. Often there 
are accessory glands whose secretion unites the sperm into packets 
known as spermatophores. There may or»may not be an external copu- 
latory organ though in the grasshopper there are a pair of these, called 
cerci. Often there are also external hard parts as in the female though, 
of course, these are not ovipositors. 

The sperm are placed in the seminal receptaculum of the female by 
the male and may remain there for many years. The queen bee only 
copulates once, and that on her first and only flight, and yet the sperm 
have remained alive so that eggs which were laid thirteen years after- 
ward were fertile. 

Fig. 225. 

Rocky Mountain locust: a, a, a, Female in 
different positions, ovipositing; b, egg-pod ex- 
tracted from ground, with the end broken 
open; c, a few eggs lying loose on the ground; 
d, e, show the earth partially removed to il- 
lustrate an egg-mass already in place and one 
being placed; /, shows where such a mass has 
been covered up. (After Riley.) 


General Biology 

There are a few insects which give birth to living young. Such are 
the parthenogenetic summer aphids, a few flies, the little bee parasites, 
Strepsiptera, a few beetles and cockroaches. But by far the greater por- 
tion lay eggs, the young then developing from these. 

When eggs develop which have not been fertilized, birth is said to 
be by parthenogenesis ( ). This occurs normally, 

at least for a number of generations, in two lepidoptera and one beetle, 
in some coccus insects and aphids, and in certain saw-flies and gall- 
wasps. It occurs casually in the silk-moth, in some grouse, locusts, and 
several other lepidoptera, seasonally in aphids, in larval life, in some 
flies [Miastor ( ), Chironomus ( )] 

and partially or "voluntarily" when the queen-bee lays eggs which 
become drones. 


Among certain tiny flies, hardly one millimeter in length and known 
as midges (Fig. 226), there are pupae which produce eggs without 

Fig. 226. Order Hymenoptera. D. 

A, gall-fly, Rhodiles rosoe, female. B, galls produced by a bug. (A, from the 
Cambridge Natural History; B, from Davenport, after Kerner.) 

C f Order Diptera. Hession fly, Cecidomyia destructor (one of the midges). 
a, larva, b, pupa. (From Davenport, after Standard Natural History.) 

D. Young paedogenetic larvae of Miastorca genus of the family Cecidomyiidae 
in the body of the mother larva. (After Pagenstecher.) 

fertilization. The larvae of the gall-gnat, the related members of this 
family, and related chironomidae likewise do this so that here we have 
a case of a granddaughter commencing to grow and develop not only 
without fertilization, but before the mother and grandmother themselves 
become full-fledged imagoes or adult insects. 

The larvae in such cases are hatched within the parent larva and 
in some cases escape by the rupture of the body. 

Such development of one, two, or three generations within the im- 
mature animal is called paedogenesis ( ), 

The Grasshopper 347 


In 1904 P. Marchal described an interesting observation. He found 
that in two small parasitic Hymenoptera ( ), a 

Chalcid ( ) — Encyrtus ( ) — 

which lay eggs in the developing eggs of the small moth Hyponomeuta 
( ) and a Proctotrypid ( ) — 

Polygnotus — which infests a gall-midge — Cecidomyid ( ) 

— larva, the nucleus of the egg of the insects divided, and each such 
particle of nucleus became a complete new embryo. A mass, or chain, 
of embryos is thus produced which lie in a common cyst and develop 
as their larval host develops. In this way over a hundred embryos may 
result from a single egg. Marchal pointed out the analogy of this phe- 
nomenon to the artificial polyembryony that has been induced in 
Echinoderms ( ) and other eggs by separating the 

blastomeres, and suggested that the abundant food-supply afforded by 
the host-larva may be favorable for this multiplication of embryos, which 
may be, in the first instance, incited by the abnormal osmotic pressure 
on the egg. 

When many embryos develop from a single egg in the way just 
described, it is called polyembryony. 

H. H. Newman has shown that in the ant-eater, armadillo, in which 
three to nine embryos commonly form in different species, all develop 
from a single egg. The fertilized egg does not split into separate parts 
but evaginates in different portions to form separate embryos. 


A true alternation of generations has been found in Hymenopterous 
gall flies (Fig. 226), in which a complete asexual generation (complete 
from egg to adult) succeeds a complete sexual generation (egg to adult), 
each generation being parasitic on a different host plant. The adults 
in each case bear no resemblance to each other ; in fact, they have not 
only been described as different species, but actually as different genera. 


The flapping of wings or the "singing" of the male grasshopper 
attracts the "unfertilized" females. The sperm are then injected into 
the female receptacle, from whence they work their way into the various 

The zygote thus formed, begins to segment mitotically, forming the 
embryo on top of the yolk close to the egg-shell. There are two 
protective membranes, the innermost being known as an amnion 
( ) or chorion ( ), and the 

outer as the serosa ( ). As soon as the embryo has 

used up the yolk as food, it is ready to hatch. 


General Biology 

However, all of this process does not take place in the body of the 
grasshopper. Soon after fertilization the female drills a hole in the 
ground with the hard portions of the ovipositor and deposits the eggs 
which are then covered. These hatch in the spring. It is here, in its 
warm underground cage, that most of the development described above 
takes place. 

"By opening and shutting the ovipositor, a hole (Fig. 225), slightly 
curved, is quickly drilled in the ground. This drilling process goes on 
until nearly the entire abdomen is buried. Ovipositing females may 
frequently be found in October. A frothy matter is first laid down from 
the cement glands, then the eggs and cement are alternatively deposited 
until some 20 to 35 eggs have been laid. Each individual egg is elongated 
and slightly curved. The female ordinarily oviposits more than once, 
averaging from 100 to 150 eggs in all. The eggs are placed side by 
side in four rows, but standing obliquely to the wall in such a way 
that all slant upward. Since they are all pushed tightly against the 
wall of the cylindrical burrow the outside rows must project beyond 
the two inner rows. In this way a channel filled with frothy matter is 
left along the tops of the rows. Such a grooved arrangement insures the 
escape of the young from the lower eggs in case those in the upper ones 
die or are delayed in hatching. 

"Each egg is covered by two membranes: (1) an outer thin, semi- 

Fig. 227. Calopt'enus Spre'tus. 

Process of acquiring wings: a, Pupa with skin^ just 
split on the back; b, the imago extending; c, the imago 
nearly out; d, the imago with wings expanded; e, the imago 
with all parts perfect, natural size. (After Riley.) 

opaque one which under a lens may be seen to be pitted or thrown into 
ridges, and (2) an inner membrane (chorion) which is smooth and thick, 
but so translucent that the young insect can be seen through it after 
development has begun. While the outer covering is easily broken, the 
inner is very resistant, requiring strong pressure between the fingers to 
crush it. 

"At hatching time in the spring the struggles of the young locust, 
together with the swelling of parts within the chorion, burst the latter, 
generally along the ventral side, and the young locust struggles out of 
its burrow. Once out, it rests a few minutes, generally lying on one side. 

The Grasshopper 349 

The limbs are at first limp and directed backward. The animal is still 
enveloped in a thin veil or pellicle which has aided it in forcing its way 
out of the ground. This covering shortly splits along the middle of the 
back and works off behind. Within an hour the locust takes its natural 
gray color. The foregoing account applies particularly to the Rocky 
Mountain locust." 

The young grasshopper (like all exoskeletonous animals), though 
able to feed immediately when its normal form has been completed, can- 
not grow until it throws off its outer covering. This ecdysis occurs 
periodically. Of course, it takes time for the new skeleton to harden, 
so that, immediately after shedding its covering, the animal is rather 
soft. The wings appear after the first molt (Fig. 227). They increase 
in size with each molt but become functional only after the final molt. 
An insect which at birth resembles its parent, but is not entirely like it, 
as the young grasshopper, is called a nymph ( ). 

The last molt takes place in the late summer. The nymph then 
"climbs up some grass stem or similar object, and, taking firm hold, 
often with its head pointing downward, remains motionless for several 
hours, till the skin swells over the head and thorax and finally splits 
open along a median dorsal line. From this old skin the new head, 
thorax, legs, wings and abdomen are slowly withdrawn while soft, ex- 
panding and hardening within half to three-quarters of an hour." 

It is then a full-fledged adult and is called imago. After the eggs 
have been laid in the fall, most of the locusts die. 


As there are more different species of insects than there are of all 
other animals combined, it is not strange that insects should be of con- 
siderable interest and importance. 

They illustrate better than any other type of animal the interrela- 
tionships and interdependence of all living things. 

Pollen is carried from one plant to another by insects (Fig. 239), 
thus permitting vegetation to grow wherever there is sufficient heat 
and moisture. This makes food more plentiful. Injurious animals and 
pests are kept down even among their own kind. For example, the swift 
little tachina fly (Fig. 240) pokes its egg between the segments of the 
grasshopper's abdomen, which egg then develops into a maggot, and 
this maggot bores its way into the interior of its host, feeding on the 
living substance as it goes. It leaves the vital organs until last, so that 
the grasshopper does not die until the maggot has abundantly supplied 
itself with nourishment. Then, too, insects furnish the most abundant 
food for birds, worms, toads, fish, and other animals. Even man has 
not hesitated to use them as food. The Bible speaks of John in the 
desert feeding on locusts and wild honey; one itself, the insect, the 
other, the product of an insect. 

350 General Biology 

In the markets of Manila large piles of grasshoppers with their 
appendages removed are offered for sale, ready for cooking. The Moors 
fry locusts in butter, and they are said to make a very palatable dish. 
In fact, many of the Indian tribes have been known to use not only 
grasshoppers, but ants as well, as a part of their diet. The natives of 
Uganda keep crickets in a warm oven for their musical sounds. In China 
it is said that fights are staged between crickets and that this is a 
favorite method of gambling. 

The larva, or grub, of the warble fly is eaten by the Dog Rib 
Indians who are fond of caribou which in turn is thoroughly infected 
with these grubs. The grubs are eaten raw- and the children consider 
them a great delicacy. 

To this list may be added moths and caterpillars, eaten by both Pai 
Ute Indians and the Australian Bushmen, while bugs, beetles and the 
eggs of these insects complete the list. The Manna of the Old Testa- 
ment is considered by entomologists to be the secretion, somewhat like 
honey, from an insect. These manna insects, now called Gossyparia 
mannifers ( ), according to Ealand, infested the 

smaller branches of Tamarix gallica ( ) in large 

numbers, sucked up sap in quantities, and exuded manna in the form of 
a sugary secretion which, in the cool of the evening, fell to the ground 
in solid form, but, after sunrise, melted and percolated the coil. 

Conditions of the past have been changed since man has learned 
to till the soil. Insects now obtain other food and their conditions of 
life have changed so that comparisons of the present with ancient times 
when men lived under vastly different conditions, are often likely to lead 
one astray. The effect of changes of conditions is particularly noticeable 
among agricultural peoples who seldom use insects as food. In famines, 
anything could be relished and it was no> wonder that such peoples 
often turned to a diet not commonly used, and then after an acquired 
taste had been brought about (just as it is known that practically no 
one likes olives the first time they are eaten, but can acquire a very 
considerable taste for them later) the children who had been fed upon 
such diet actually relished it as they grew up. No better proof of this 
could be found than the fact that pigeons and rabbits never normally 
eat meat, but, if they are fed meat alone from birth, they will die rather 
than eat a normal pigeon's or rabbit's food when they have become 
fully grown. 

In addition to being used as food, insects have formed a great source 
from which various oils and other medicinal substances have been 
abstracted from time immemorial. All historical literature is filled with 
references to this use of insects. 

Over against this beneficial use of insects may be placed the great 
devastations in our own country by the periodical locusts which sweep 
grain fields bare before them, and other crop-injuring pests, such as boll 

The Grasshopper 


weevils, which injure thousands of dollars worth of cotton annually, 
while almost every type of grain has some sort of insect which uses 
such grain as its food. 

As carriers of developing eggs or various immature forms of para- 
sites, insects are now known to do great injury to man as well as to the 
animal world at large. The classic example is that of the anopheles 
mosquito, which carries malaria, and the tse-tse fly, already referred to 
as the carrier of the germ of sleeping sickness. 

Fig. 228. 
Lice — both animal and plant. 

A. Female of flea, Pulex irri- 
tans, infesting man. (After 

B. Sarcoptes 
female itch mite. 


C. Order A carina. Harvestmites 
or "chiggers." Leptus irritans on 
the right; L. americana on the left. 
(From Osborn, after Riley.) 

D. Common cat and dog flea (Pulex ser- 
raticeps) : a, Eggs; b, larva in cocoon; c, 
pupa; d, adult; e, mouth parts of same from 
side; /, labium of same from below; g, an- 
tenna o£ same; all much enlarged. (Howard, 
Bull. U. S. Dept. of Agriculture, 1896.) 

Rat Fleas.— It is believed that in tropical 
countries the disease germs of the bubonic 
plague may be transmitted from rats to men 
by the bites or punctures of rat fleas. 

E. Phylloxera vastatrix: a, _ Leaf with 
galls; b, section of gall showing mother 
louse at center with young clustered about; 
c, egg; d, larva; e, adult female; /, same 
from side. (a, Natural size; b-f, much en- 
larged.) (Marlatt.) 





ta^ 16 



Wl "**"**-' 


F. Phylloxera vastatrix: G. Pediculoides ventricosus, H. Head and Pronotum of (a) dog 

a, Root-galls; b, enlarge- male. Grain louse which flea; (b) of cat flea; (c) hen flea, 

ment of same, showing affects farmers and thresh- (After Rotschild.) (d) Nycteridiphilus 

disposition of lice; c, a ers. (After Braun.) (Ishnopsyhus) hexactews, (After Ou- 

root-gall louse much en- demans.) 
larged. (Marlott.) 

352 General Biology 

Lice (Fig. 228), and other so-called vermin (all of these belong to 
the insect group), are not only injurious to higher forms of life by their 
acts, but are dangerous carriers of disease. 

The common house fly carries dirt and filth from the garbage can 
and manure pile to the food it lights upon, as well as to the baby's 
drinking bottle. In the filth thus deposited, there are hundreds of tiny 
eggs and seeds, which require only the necessary moisture and heat 
of the interior of the human or animal body to begin developing. This 
is the common way in which typhoid fever is carried. One can hardly 
get this disease, unless some excreted matter from a typhoid patient has 
been taken into the intestinal tract. 

An excellent way to demonstrate the fact that insects' eggs are 
on our foodstuff is this : Take any fruit, such as bananas, apples, cher- 
ries, or grapes, and place the fruit in a bottle plugged with cotton, so 
that air, but nothing else, may pass in. In a short time, various forms 
of animal life will be found therein. As these forms of life hatched 
from eggs, the eggs must have been on the fruit before it was placed 
in the bottle. It is of value to note that even after one has washed the 
fruit well, such hatching will almost always occur. This shows how 
thoroughly insects fasten their eggs either on or into the surface struc- 
tures of fruits. 

When different kinds of crops are planted, different kinds of insects 
will thrive, and those alone will survive which have a sufficient food 
supply. Those not feeding on the new plants, either leave for more 
satisfactory fields or die. If it is remembered that the flesh of a duck, 
which feeds on fish, tastes quite different from that of one not so fed, 
it will be seen that the food of an animal makes a great chemical differ- 
ence in the body tissues. It can then be understood how different dis- 
eases may come forth when parasites change their food and environment. 
If the food it eats makes a chemical difference in the flesh of an animal, 
it also means that, if a new chemical substance in a parasite is poisonous 
to man, then the same parasite, when feeding on one food, may not 
be poisonous and not cause disease, whereas when feeding on another 
type of food, such chemical poison may cause disease. Then there is 
the interesting fact that many diseases of birds will not affect a frog 
normally when such disease germs are injected, but, if the frog is placed 
in an incubator where its blood is kept at the same temperature as that 
of the bird from which the disease is taken, the disease will develop. 
This illustrates how different temperatures change the susceptibility of 
different organisms to different diseases. 

The animals commonly called grasshoppers are of varying types 
(Fig. 229). The true grasshopper is long-horned; that is, it has two 
antennae as long or longer than its entire body. The family to which 
these belong is known as Locustidae, while the short-horned grasshop- 
pers belong to the family Acridiidae. 

The Grasshopper 


In America the Rocky Mountain Locust is the one which does the 
great damage to crops. The exact time of laying and hatching eggs 
varies somewhat with the region of the country. 

Often the young, until after the second or third molt, content them- 
selves with feeding on whatever food is close at hand, but as soon as 
this food becomes scarce, the animals congregate and, as Ealand says, 
they march across the country in solid bodies, sometimes as much as a 
mile wide, "devouring every green crop and weed as they go. During 
cold or damp weather and at night they collect under rubbish, in stools 
of grass, etc., and at such times almost seem to have disappeared ; but 
a few hours of sunshine brings them forth as voracious as ever. When, 
on account of the immense numbers assembled together, it becomes 
impossible for all to obtain green food, the unfortunate ones first clean 

out the underbrush and then 
feed upon the dead leaves and 
bark of timber lands, and have 
often been known to gnaw 
fences and frame buildings. 
Stories of their incredible ap- 
petites are legion. A friend 
informs the author that he still 
possesses a rawhide whip 
which they quite noticeably 
gnawed in a single night. 

"By mathematical compu- 
tation it has been shown that 
such a swarm could not reach 
a point over thirty miles from 
its birthplace, and as a matter 
of fact they have never been known to proceed over ten miles." 

There are other species and genera which do not migrate from their 
native haunts. Many ingenious ways have been used to exterminate 
them. Certain fungus growths on plants, which the grasshopper uses 
for food, are fatal to him. So, too, is the little tachina fly already men- 
tioned. In some regions, agriculturists develop such fungus growth 
and flies to assist in controlling the injurious insects. 

The effect of a difference of temperature on insects is well illustrated 
by the fact that there is only one annual generation of grasshoppers in 
New England while there are two in Missouri. 

Ditches are often dug so that the animals will fall into them, or 
kerosene emulsion is poured on water standing about, or placed in 
simple trough-like wooden movable ditches. Even if the grasshopper 
crawls out of the oil, it dies shortly after. 

For the control of grasshoppers, see any of the books on economic 
entomology mentioned at the end of Chapter XXIV. 

Fig. 229. Long- and Short-Horned Grasshoppers. 

A. Order Orthoptera. Katydid, Microcentrum 
retinerve. (From Sedgwick's Zoology, after Riley.) 

B. Red-legged grasshopper (Melanoplus femur- 
rubrum); Ab, abdomen; Ant, antennae; E, eye; M, 
mouth; T , thorax; S, spiracles. 



THE honey bee (Fig. 230) has been studied and written about for 
centuries as one of the most interesting of insects. It lives a de- 
cidedly complex social life and has lent to proohets and teachers 
of all times many lessons for human conduct. 

The bee is intensely specialized in almost all parts of its body, and 
as such is of great value to any comparative study of the arthropods. 

Fig. 230. 

Hive bees and comb. A, Worker; K, queen; D, drone; 1, 
worker with cells filled with honey and covered; 2, cells contain- 
ing eggs, larvce, and pupae; 3, cells containing pollen; 4, below 
4 are regular cells; 5, drome cells; 6-10, queen cells. (After 

Foremost in rank in the hive is the queen. She is the mother of 
every member of the hive, for she alone, of all the inhabitants, lays eggs. 
With her, in the summer time, there are some sixty thousand workers 
and several hundred drones. The latter are killed during the winter. 
The abdomen of the queen is longer than that of a worker, and there 
is no pollen basket on the tibia of her hind legs. 

The drone is the male. He lives upon the food gathered by the 
females. His body is heavy and broad, and no pollen baskets are found 
on the hind legs. His eyes are larger than those of either queen or 

The worker is an undeveloped female, which can, however, by proper 

The Honey Bee and the Fly 


food, nourishment and care, become a queen in case the old queen dies. 
The workers are smaller than either queen or drones. They are the ones 
usually seen hovering about flowers. 

Bees have mouth parts (Fig. 231), modified both for biting and 
sucking, and two pairs of membranous wings. 

Fig. 231. 

A. Front view of the head and mouth 
parts of a bee. a, Antenna; m, mandible; 
g, labrum and epipharynx; mx.p., rudiment 
of maxillary palp; mx., lamina of maxilla; 
lp., labial palp; /., ligula; b., bouton at end. 
The paraglossae lie concealed between the 
basal portions of the labial palps and the 
ligula. (After Cheshire.) 

B. Side view of mouth parts of the honey 
bee, Apis Mellifera. a, base of antenna; br, 
brain; c, clypeus; h, hypopharynx; /, labrum; 
lp, labial palpus; m, mentum; mo, mouth; 
mx, maxilla; sm, submentum. (After Chesh- 

C. Tongue of honey 
bee. p., protecting bris- 
tles; s., terminal spoon; 
t., taste setae. (After 


The body is divided into head, thorax, and abdomen. (Fig. 213.) 
The body is covered with a skin or cuticle which is composed of a thin 
chitinous layer produced by the secretion from the cells lying beneath 
it. This serves as a protection, but it is cast off at various intervals 
during the early stages of growth. 

There are a pair of large compound eyes and three ocelli or simple 
eyes. The arrangement of the ocelli are somewhat different in queen, 
worker, and drone. Two feelers (antennae) project from the front of 
the head. 

The mouth is made up of an upper lip or labrum, an epipharynx, a 
pair of mandibles, two maxillae, and a labium. This last mentioned is 
the under lip. 

The labrum is joined to the clypeus (the dome-shaped portion of 


General Biology 

the skull), (Figs. 217 and 231), lying just above it. The epipharynx is 
the fleshy projection extending beneath the labrum. It serves as an 
organ of taste. The jaws, or mandibles, lie on each side of the labrum, 
being notched in the queen and drone, and smooth in the worker. 

The labium lies medially and extends downward from beneath the 

labrum and is quite compli- 
cated. The sub-mentum, which 
is triangular in shape, joins the 
labium to the back of the head. 
The mentum lies next to the 
sub-mentum. The mentum is 
chitinous and contains muscle. 
The tongue, or ligula, lies im- 
mediately beyond the mentum. 
The tongue has a spoon-shaped 
end known as a bouton. A 
labial palpus lies at each side 
of the tongue, while tiny hairs, 
used as organs of taste and 
touch, as well as for gathering 
nectar, are arranged in regular 
rows upon it. 

The lower jaws or maxil- 
lae extend over the mentum on 
both sides. There are stiff hairs 
on their edges, and maxillary 
palpi on each side. 

The thorax is divided into 
prothorax, mesothorax, and 
metathorax (Fig. 213), the last 
two divisions each supporting 
a pair of wings, while hairs, 
which are used in gathering 
pollen, cover the outside of the 
entire thorax. 

Fig. 232. 

Legs of worker honey-bee. A., outer side of 
metathoracic leg; p., metatarsus; t., tarsus; ti., tibia. 
B., inner side of metathoracic leg. c, coxa; p., meta- 
tarsus^ t., tarsus; ti., tibia; tr., trochanter; wp., 
wax pinchers. C, prothoracic leg. b., pollen brush; 
eb., eye brush; p., metatarsus; t, tarsus; ti, tibia; v., 
velum. D., mesothoracic leg; lettering as in C. s., 
pollen spur. E., joint of prothoracic leg; lettering 
as in C. P., teeth of antenna comb. C, transverse 
section of tibia through pollen basket. fa., pollen; 
h., holding hairs; n, nerve. H., antenna in process 
of cleaning. a., antenna; s., antenna comb; /., sec- 
tion of leg; s., scraping edge of v., velum. (From 
Root, after Cheshire.) 

The legs of the bee are 
highly specialized (Fig. 232). 
The prothoracic legs have both 
femur and tibia covered with branched hairs which are used in gather- 
ing pollen. A pollen brush made up of curved bristles is seen at the 
distal end on one side of the tibia. This brush is used to brush up the 
pollen which has been loosened by some of the coarser spines. 

On the other side of the tibia, a flat movable spine, known as the 
velum, fits over a curved indentation in the first tarsal joint. The whole 

The Honey Bee and the Fly 


structure, brush and velum, is known as the antenna cleaner, while the 

row of teeth lining the indentation is called the antenna comb. 

The antennae are cleaned by being pulled through the indentation 

between the teeth and the edge of the velum. 

On this first tarsal joint also, there is found a row of spines called 

the eye brush. This structure is used to brush out pollen which has 

lodged about the compound eyes. 

On the last tarsal joint of each leg there is a pair of notched claws 

by which the insect holds on to rough surfaces. Between these claws 

there is a fleshy glandular lobule, known as the pulvillus, which is cov- 
ered with a sticky secretion from the 
glands. It is by this sticky substance 
that the insect can attach itself to 
smooth surfaces. Then, too, tactile or 
touch hairs are present. 

The mesothoracic legs do not have 
an antennae cleaner, but at the distal 
end of the tibia there is a spur which 
is used to pry the pollen out of the 
pollen baskets on the third pair of legs, 
as well as to clean the wings. 

The metathoracic legs are prob- 
ably the most interesting, in that they 
possess a pollen basket, a wax pincer, 
and pollen combs. The pollen basket 
is a concavity in the outer surface of 
the tibia. There are rows of curved 
bristles along the edges. Pollen is 
stored in this basket. The filling takes 
place by the pollen combs scraping out 
the pollen from the hairs on the thorax 
into the basket on the opposite leg. 

Because of their pincer-like ap- 
pearance the opposed ends of the tibia 
and metatarsus of the hind leg were 
formerly called "wax-pincers." The row of wide spines on the end of 
the tibia forms the pecten; the flat, tamp-like plate at the end of the 
metatarsus opposed to the pecten, is the auricle. This jaw-like structure 
is used to transfer pollen to the pollen-basket. The pecten is scraped 
downward over the pollen comb of the opposite leg, and the pollen thus 
secured is pushed upward into the pollen-basket from below by the 
rising auricle as the leg is flexed. 

As already stated, a pair of membranous wings are attached to the 
mesothorax and a pair are attached to the metathorax. There are hollow 
ribs, called nerves or veins, passing through each wing. Often a row 

Sting of worker honey-bee. b., barbs on 
darts; i., k., I., levers to move darts; n., 
nerves; p., sting-feeler; pg., poison gland; 
ps., poison sac; sh., sheath; 5th g., fifth 
abdominal ganglion. (From Packard, 

after Cheshire.) 

358 General Biology 

of little hooklets on the anterior margin of the hind wing is inserted 
into a trough-like fold in the posterior margin of the fore wing and thus 
joins them together. 

The abdomen is made up of six segments, each segment consisting 
of a tergum or dorsal plate, and sternum or ventral plate. A pair of wax 
glands is located on each of the four hindermost sternal plates. Both 
queen and worker possess a sting (Fig. 233) at the end of the abdomen, 
while the drone possesses a copulatory organ instead. There are also 
slit-like openings of the reproductive system and an anal opening in 
queen and worker. 

The sting has a pair of sting feelers by which the bee seems to 
choose a favorable location for the deposit of the sting. Two barbed 
darts are then sent out. There is a sheath which guides the darts and 
aids in conducting the poison. The poison is secreted by a pair of 
glands, one acid and one alkaline, and it is then stored in a reservoir. 
It is commonly believed that if a bee stings it dies. This is not neces- 
sarily true ; but, very often a part of the intestine and the poison glands 
are pulled out of the body with the sting, and then, of course, the insect 
cannot live. 

Queens usually do not sting except in combat with other queens. 



Beginning at the anterior end, the digestive system (Fig. 234), is 
made up of mouth, oesophagus or gullet, honey-sac or honey-stomach, 
true stomach, small intestine or ileum, and large intestine or colon. 

The oesophagus passes through the thorax and is expanded into a 
honey-sac at the anterior end of the abdomen. A stomach-mouth with 
four triangular lips is found at the posterior portion of the honey-sac. 
A number of bristles extends backward from the top of the lips. If the 
alimentary canal be placed in a one-half of one per cent salt solution 
immediately after the bee is killed, these lips will open and close for 
about thirty minutes. Both circular and longitudinal muscles surround 
the lips. 

The glands in the walls of the stomach secrete digestive juices which 
change the food into chyme. Part of this is absorbed and part forced 
back into the ileum by muscular contractions. Here undigested food is 
dissolved and also absorbed, while that which is not digested is thrown 
into the colon, and from there, out of the body. No faeces are deposited 
in the hive if bees are kept in proper condition. 

Two pairs of salivary glands may be found: one pair within the 
head lying against the cranium, and one pair in the ventral portion of 
the anterior half of the thorax. The substances secreted from these 
glands are weakly alkaline and are poured out upon the labium. Here 
they act on the food as it is ingested. 

The Honey Bee and the Fly 



The blood of the honey bee is quite like that of the crayfish and 
grasshopper in being colorless and containing amoeboid corpuscles. 
The amount of oxygen it contains is not very great. A "respiratory 
pigment" — hemocyanin, a copper compound, gives the blood a faintly 
bluish color, which is especially perceptible when some dozen or more 
drops of blood are obtained. The blood acts as an aid in the fixation 
and distribution of oxygen. 

The crayfish is also like the bee in that it has a dorsal blood vessel 
and many sinuses, but the bee's circulatory system is even less complete 
than that of the crayfish. 

The heart, or dorsal vessel, is a tube in the median dorsal region 
just below the surface, closed posteriorly and open in the head-region. 
The walls are muscular and the heart contracts at intervals. 

The blood itself enters through five pairs of ostia, one into each of 
the five compartments into which the heart is divided. Each compart- 
^,-w- ment is called a ventricle. Each 

contraction sends the blood toward 
the heart. There are valves which 
prevent it from flowing backward. 
It then passes through the various 
spaces in the body to bathe the 
tissues. As the blood passes ven- 
trally, it is gathered into the peri- 
cardial sinus, and, when the muscles 
surrounding this sinus contract, the 
blood is forced through the ostia 
back into the heart. 


Fig. 234. 

A. Internal organs of the honey-bee. bt., 
malpighian tubules; c.s., true stomach; dv., 
dorsal vessel; e., eye; g., ganglia of nerve 
chain; hs., honey sac; li., rectum; lp., labial 
palpus; mesa, t., mesothorax; meta, t., meta- 
thorax; tux., maxilla; n., nerves. No. 1, 
No. 2, No. 3, salivary glands; oe., oesophagus; 
p., stomach mouth; pro.t., prothorax; si., 
small intestine (ileum) ; v., ventricles of dorsal 

B. Ideal transverse section of an insect. 
h., dorsal vessel; i., intestine; «., ventral 
nerve-cord; t.t., stigmata leading into the 
branched tracheal tubes; w.w., wings; a., 
coxa of one leg; b., trochanter; c, femur; d., 
tibia; e., tarsus. (After Packard, A, from 

360 General Biology 


Along each side of certain thoracic and abdominal segments there 
appear openings called spiracles (Fig. 215). It is through these openings 
that the bee breathes. One pair of these spiracles may be found in the 
prothorax, one pair in the metathorax, and five pairs in the abdomen. 

The spiracles open into little tubes known as tracheae which unite 
in turn with other tubes running in a longitudinal manner. These longi- 
tudinal tubes are called the trunks, and from the trunks many branches 
are given off to all parts of the body. The tracheary tubes (though 
only one cell in thickness) have thickened rings arranged spirally, and 
it is these rings which keep the tubes open. 

Air-sacs are found in the abdominal region. These are expanded 
portions of the tracheae and probably make the bee lighter as it flies, 
for the bees can apparently increase and decrease the size of the air-sacs 
at will. There are tiny valves in the spiracles and the bee takes in and 
expels air by expansions and contractions of its abdomen. Hairs sur- 
round the spiracles so as to prevent dust from entering. The rate of 
respiration increases with the fatigue of the insect. Air is carried 
directly to the tissues through the tracheae so that there is no need for 
a lung system in which blood and oxygen must mix. 


There are Malpighian or urinary tubules (Fig. 234, A) which are 
long, fine, hair-like structures, opening into the anterior end of the 
intestine. These are the excretory organs. Excretions are taken from 
the blood in the form of urates, and pass through these urinary tubules 
to the intestine from whence they are thrown out of the body with the 


The nervous system (Fig. 214, 235) of the bee is made up of a chain 
of paired ganglia with two groups of smaller ganglia. The first are 
called the stomatogastric and the latter the sympathetic ganglia, re- 
spectively. These ganglia are made up in turn of the following masses 
of nerve tissue: two in the head, two in the thorax, and five in the 

Each mass is composed of two ganglia which lie side by side, and 
these ganglia are connected with the mass in front and behind by two 
nerve cords. Only the brain (the most anterior pair of ganglia), also 
called the supraoesophageal ganglia, lies dorsal to the digestive tract. 

The compound eyes, the ocelli, the antennae, and the labrum, are 
connected with the brain by nerve twigs, while the mandibles, labium, 
and other mouth-parts are connected with the suboesophageal ganglion 
lying directly beneath the oesophagus. 

The Honey Bee and the Fly 


The most anterior ganglia in the thorax innervate the muscles of 
the first pair of legs, while the posterior thoracic ganglion is larger and 
composed of several ganglia which have grown together. From the 
fore part of this latter ganglion, nerves run to the fore wings and middle 
pair of legs, while twigs from the posterior portion of this same ganglion 
pass to the hind wings and legs. 

The organs and walls of the abdominal region are supplied by twigs 
from the various abdominal ganglia; but, as with most animals, the more 
posterior abdominal ganglia are the larger. 

The stomatogastric portion of the nervous system is composed of 

tferv&s io 

^ upper mouth parts 

-Ani&nnal n&rvz 
"—Optic n&rue. 

-lateral ganglion, 

Drain — -^vv 




l&curr&nl _ 

Fig. 235. 

A. Nervous system of honey-bee, at a., and of 
its larva, at b., showing the simple type of the larva 
and the specialization in the adult due to fusion of 
the ganglia. (From Sanderson and Jackson, "Ele- 
mentary Entomology," by permission of Ginn & Co.) 

Nerua io 
-- salivary 


B. Sympathetic nervous system of 
an insect, diagrammatically represented. 
(After Kolbe.) 

C. Nervous system of the head of cock- 
roach, a., antenna! nerve; ag., anterior later- 
al ganglion of sympathetic system; b, brain; 
d., salivary duct; /., frontal ganglion; h., 
hypopharynx; /., labrum; li., labium; m., 
mandibular nerve; vnx., maxillary nerve; nl., 
nerve to labrum; nli., nerve to labium; o., 
optic nerve; oc, oesophageal commissure; oe., 
oesophagus; pg., posterior lateral ganglion of 
sympathetic nervous system; r., recurrent 
nerve of sympathetic system; s., suboeso- 
phageal ganglion. (After Hofer.) 

many small ganglia which are in 
direct connection with the organs 
of digestion, circulation, and respira- 
tion, while the sympathetic nervous 
system is made up of the many 
fibers which pass to all parts of the 
body from the triangular ganglia 
lying in each segment. 


These have already been dis- 
cussed very thoroughly under the 
general term, 'The Senses of In- 
sects," in Chapter XXIII. 


General Biology 


As in the crayfish, the muscles of the honey bee are attached to the 
inner walls of the body. The number of muscles is very large. The 
largest muscles are those which move the wings and legs. 

Muscles are both voluntary and involuntary. A good example of 
the latter has already been noted in the experiment suggested of placing 
a portion of the intestine in a one-half of one per cent salt solution when 

the lips of the stomach-mouth will open 
and close for some time. 

Insects usually have much greater 
muscular strength proportionately than 
larger animals. This is accounted for by 
the fact that the weight of muscle in- 
creases as the cube of its diameter, while 
its strength increases only as the square 
of its diameter. 


Only the queen (Fig. 236, A) can lay 
eggs, although the workers have rudi- 
mentary ovaries. 

The two- ovaries almost fill the ab- 
domen of the queen. Each of the ovaries 
is made up of a great number of ovarian 
tubules which contain eggs of different 
sizes. The eggs pass into the oviduct 
from the tubules, thence into the vagina 
and out of the body through the genital 

There is an opening into the vagina 
which connects with the spermatheca, or 
sac, in which the sperm are stored, and 
sperm from this sac may apparently be 
released at will by the queen as the eggs 
pass through. If the sperm is not re- 
leased, the egg is not fertilized and then 
drones hatch. Only females hatch from 
fertilized eggs. 

In the drone (Fig. 236, B) there are 
two testes made up of several hundred 
spermatic tubules in which the sperm are 
formed. A pair of fine tubes, called vasa 
deferentia, connect these spermatic tubes 
with the seminal vesicles. These latter 

Fig. 236. 

A. Reproductive organs, sting, and 
poison gland of queen honey-bee. AGL, 
acid gland; AG ID., duct of acid gland; 
BGL, alkaline gland; Ov., ovary; ov., 
ovarian tubules; OvD., oviduct; Psn.- 
Sc, poison sac; Spm., spermatheca; 
Stn., sting; StnPlp., sting feeler; Vag., 

B. Reproductive organs of drone 
bee, dorsal view, natural position. 
AcGl., accessory gland; B., bulb of 
penis; EjD., ejaculatory duct; Pen, 
penis; Tes., testis; vDef., vas deferens; 
Ves., seminal vesicle; tt., un., yy., zz., 
parts of penis. (From Snodgrass, 
Tech. Series, 18, Bur. Ent., U. S. 
Dep't of Agric.) 

The Honey Bee and the Fly 


in turn open into a pair of large mucous glands which unite. It is at 
this union that the ejaculatory duct begins. This duct ends in the 
copulatory organ. 

The sperm of the male are placed in the spermatheca (seminal re- 
ceptaculum) of the queen by a single drone, where they remain alive 
for many years, in fact as long as the queen lives and lays eggs. While 
the average life of a queen is probably from three to four years, there 
is on record a queen which continued laying fertile eggs for thirteen 
and a half years. 

About five to eight days after' emerging from the comb-cell, a queen 
leaves the hive. First, she crawls about and takes very short flights, 
and then goes on a nuptial trip of about thirty minutes. One of the 
drones copulates with her during the nuptial trip, after which the queen 
returns to the hive. 

The eggs are bluish-white and oblong in shape. They are fertilized 
just before leaving the queen's body. The eggs are deposited at the base 
of the cells and then fastened into position in the cells by a secretion. 
Fertilized eggs are laid in cells that have already been arranged to 
receive them, some being in queen cells, and some in worker cells, while 
unfertilized eggs are placed in drone cells. But there seems to be 
evidence that mistakes are made, and the right type of egg is not always 
placed in the right cell. 


After the nuclei of the sperm and egg have united into a single 
nucleus, a chitinous covering, the chorion, surrounds the entire egg. As 
cleavage takes place, no definite cell walls appear. This means that a 
great mass of protoplasm is present with many nuclei. These nuclei 

migrate to the periphery to form a 
single layer of cells, called the blas- 
toderm, while the remaining portion 
of the yolk remains as yolk-sub- 
stance until it is converted either 
into food for the developing em- 
bryo, or into further cellular sub- 

A germ-band or primitive streak 
(Fig. 237) now forms on one side of the egg where the blastoderm 
becomes thickened. This is to become the ventral side of the bee. The 
brain develops separately. A median groove arises in the germ-band, 
and so two germ layers are formed, an outer layer called the ectoderm, 
and an inner known as the entomesoderm. It is the latter layer from 
which both entoderm and mesoderm arise. The germ-band then grows 
around the entire egg. 

It is of interest to know that, while the antennae and four pair of 

Fig. 237. 

Cross section of germ-band of Clytra at 
^astrulation. g., germ-band; i., inner layer. 
(After Le'caillon.) 

364: General Biology 

appendages can be seen near the anterior end of the embryo, one pair 
of the anterior appendages disappear and the others become mouth 
parts. Then, three pair of appendages develop on the thorax, all of 
which disappear before hatching, 


The life-history of the bee is divided into four periods : egg, larva, 
pupa, and adult or imago. 

Queens, workers, and drones remain in the egg three days, but the 
queens remain in the larval stage five and a half days, and in the pupal 
stage seven days, while the workers remain in the larval stage five days, 
and in the pupal stage thirteen. The drones remain in the larval stage 
six days, and in the pupal stage fifteen days. 

During the fourth day the larva hatches from the egg as a white, 
footless, soft, grub-like form floating in "bee-milk" (also called "royal 
jelly"). This "milk" is composed of digested honey and pollen with 
probably some glandular secretions. The "milk" is formed in the true 
stomachs of special "nurse" workers who place it in the cells. 

All larvae are fed this royal jelly for about three days by the nurse 
workers, after which a change takes place. Those which are to become 
workers are fed honey and digested pollen, while those which are to 
become queens alone continue to get the richer royal jelly until they 
change to the pupal stage. The drone larvae, after the fourth day, 
receive undigested pollen and honey. 

The young larvae grow rapidly and shed their exoskeleton several 
times. In fact, during the last molt, even the lining of the alimentary 
canal and all its contents are shed with the exoskeleton. 

Some five or six days after hatching, the nurse worker places a 
quantity of food in the cell with the larva and places a cap on the cell. 
The larva spins a cocoon of silk about itself some two or three days 
later. It is now in a resting stage and is called the pupa. 

The spinning-glands are in the mouth region, and later become the 
salivary glands of the adult. 

Almost the entire structure is made over during this pupal stage, 
and the full-fledged bee emerges in its adult form and shape. 


As the queen emerges from the pupal stage the eggs have not yet 
distended her abdomen. She is, therefore, about the same size as a 
worker. As soon as she becomes accustomed to her surroundings, she 
starts on a hunt for other queen cells. She breaks through these and 
stings the pupa within or tears the cell down and lets the workers remove 
such destroyed structures with the other debris. There is thus only 
one queen left. It is after this time that the nuptial-flight, already 

The Honey Bee and the Fly 365 

mentioned, takes place. By the ninth or tenth day she is busy laying 
eggs. The number of eggs laid, or at least the rapidity with which 
eggs are laid, is determined by the amount of food the workers bring 
home. More eggs are laid when more food is obtained. 

The workers, when young, act as nurse maids for a week or two 
before taking up the regular duties of gathering food. Some of these 
also defend the hive against outside attacks, clean the hive, and even 
go scouting to find suitable new quarters before swarming. 

^he workers really work themselves to death, and probably live 
only some five or six weeks. New ones are being hatched continually 
to keep the normal number of bees in the hive. Those which hatch in 
the fall may live five or six months. 

If a queen should die, any one of the workers may with proper 
feeding, be able to develop and lay eggs, but in such cases the new queen 
would not have had the nuptial-flight, and therefore no eggs would be 
fertile. Consequently drones alone are hatched from the eggs. 

Drones hatch in the same way that queens and workers do, but take 
no part in the work of the hive. One of them alone acts as queen- 
consort. As soon as food is scarce, they are starved to death and their 
dead bodies are removed with the remaining debris. At such a time 
even the drone pupae, larvae, and eggs are destroyed. 

As new bees are constantly being hatched, the hive may become 
overcrowded. When this occurs, it is the old queen which collects 
several thousands bees about her and goes through a complicated prepa- 
ration to start a new colony. Scouts are sent out to seek a fitting loca- 
tion, and after first settling on a tree-branch or other object in a very 
dense cluster, the whole colony takes up its new abode. 

The cells in the hive are made of wax. Those which are to have 
eggs placed in them, are hexagonal in shape, although a careful exami- 
nation will show they all vary slightly from one another. The cells 
which are to contain honey, are rounded. 

The wax is produced by a secretion from the smooth paired patches 
on the ventral surface of the abdominal metameres, called wax-glands. 
The process gone through is as follows : The bees gorge themselves 
with honey. Great clusters of such bees then hang from the top of the 
hive for several hours, and thin scales of wax form on the plates. These 
scales of wax are then removed by the hind legs, while the fore-legs 
transport the wax to the mouth. Here the wax scales are mixed with 
saliva and kneaded by the mandibles. The wax is then ready either to 
repair old cells or build new ones. 

The cells may be built especially for honey or for breeding, but 
often drone cells, even when the cocoon is still present, are used for 
honey cells. However, cells made especially for honey have the open- 
ings somewhat above their bases so that the honey will not run out 

366 General Biology 

The cells which fasten the comb to the top and sides of the hive are 
called attachment cells. 

Bees gather nectar (not honey) from flowers. The maxillae and 
the labial palpi form a tube through which the tongue can move back- 
ward and forward. As the epipharynx is lowered, a definite passage 
connects this tube with the oesophagus. The nectar itself becomes 
attached to the hairs on the tongue, and is forced upward by pressing 
maxillae and palpi together. It is then swallowed into the honey-sac 
where the necessary chemical changes, which convert it into honey, take 
place. Here it is retained until the bee reaches the hive, when it is 
regurgitated into the cells made to receive it. As there is much water 
in newly-formed honey, the cells are left open until the water is con- 
siderably evaporated. This is called the "ripening process." When the 
honey is "ripe" the cell is capped with wax. 

The bees keep their wings moving while in the hive both to keep 
air circulating and (in winter) to produce heat. 

About thirty to fifty pounds of honey are produced a season by one 
hive if conditions are favorable. 

As honey lacks proteins, bees gather pollen by means of their mouth 
parts and legs, and mix it with either saliva or even nectar to make it 
sticky. It is then placed by the hind legs in the pollen baskets. As 
the bee enters the hive, it backs up to a cell in which a larva is placed, 
and scrapes the pollen into such cell by aid of the spur already men- 
tioned. The deposited substance is known as "bee-bread." The young 
workers then pack this bee-bread into the cells by using their heads as 

Still another substance, known as propolis or "bee-glue," is gathered 
by bees for the purpose of filling up cracks, for strengthening weak 
parts, or even, probably, as a sort of varnish. Propolis is merely the 
resinous material gathered from various plants which is then inserted 
into the pollen basket. When propolis is brought to the hive by a worker, 
another worker removes it from the gatherer. It is this other worker 
which also applies it where needed. 

In warm, dry weather water is often sucked into the honey-sac from 
dew, brooks, or ponds, and then carried to the larvae in the hive. In 
cool weather enough water usually condenses in the hive. In fact, so 
much moisture may condense as to injure the occupants. 

All debris is removed immediately so that cleanliness is always 


There is a bee-moth, Galleria mellonella, which, when it can find 
an entry, lays its eggs in the hive. The larvae then feed on pollen, 
cocoons, and even cast-off larval skins. They burrow into the comb and 
line their burrow with a silk which protects them from the bees, much 
as a spider's web can either keep out or entrap insects. 

The Honey Bee and the Fly 


There are also bee-lice which attach themselves to the queen and 
weaken her by sucking the juices from her body. The bee-lice, while 
common along the Mediterranean Sea, are uncommon in America. 
Spiders often catch bees in their webs. 

Other insects such as dragon-flies, ants, and wasps may attack bees. 
Toads and lizards also attack them, but these latter can be removed to 
some distance from the hive and will then serve the important function 
of devouring really noxious insects. 

Mice prey upon pollen, honey, and even bees in the winter time. 
One may note here, as we have already noted in the discussion of the 
relation of insects to man, that there may be various ways of insuring 
a "balance in nature." As cats devour mice, and mice bees, the number 
of cats may be the deciding factor of the number of bees there are in a 
given neighborhood. In fact, Huxley 
even suggested that this idea could be 
carried still further by considering the 
number of old maids who were fond of 
cats, these cat lovers then becoming the 
deciding factor as to the number of bees 
a given region might have. 

Various diseases also afflict bees. 
These are probably largely of a bacterial 
nature brought about by too long con- 
finement in the hive. Once a disease has 
taken hold of a hive, it may infect any or 
all other hives in the region. 


It has been found that among butter- 
flies, ants, and bees, it is not uncommon 
to have an abnormal individual which has 
male characteristics in one part of its 
body and female characteristics in an- 
other. The term gynandromorphs (Fig. 

Fig. 239. 

Salvia sp. (One of the Labiatae.) a., 
flower bud; b-f., various views of the open 
flower; an., anther; St., stigma; x., projec- 
tions near the base of the filaments. Tht lead 
pencil is made to imitate an insect visiting 
the flower for pollen. By pressure at the base 
Dt the filaments, the anthers are brought into 
contact with the surface of the pencil, which 
thus becomes covered with pollen. When the 
next flower is visited the stigma, having then 
bent down and spread apart, .eceives the 
pollen from the other flower. Thus is ac- 
complished cross-pollination. In b., before the 
visit of the insect, the stigmatic surfaces are 
still in contact, so that pollination is not pos- 
sible. (From C. Stuart Gager's "Funda- 
mentals of Botany" by permission of P. Blak- 
iston's Son & Co., Publishers.) 

Fig. 238. 
External appearance of gynandromorph. 
Lateral hermaphroditism of gypsy moth. Left 
side female; right side male. (After Tasch- 

368 General Biology 

238) has been given such individuals. The more common form such 
gynandromorphs assume is that the anterior part of the body may be 
one type and the posterior another, or the entire right side may be of 
one sex and the entire left side of another. 


Bees are particularly valuable in bringing about cross fertilization 
of flowers. In fact, the bumble bee is about the only insect visiting red 
clover, which has its mouth parts long enough to reach down for the 
nectar of that plant, so that if it were not for the bumble bee, red clover 
would probably not grow at all. 

Orchards which have hives of bees usually show a better harvest 
of fruit than those without hives. 

It is probably color, odor, and the structure of both insect and plant 
which determine which plants are visited most. 

Many plants are so constructed that an insect entering the flower 
for nectar comes in contact with the pollen of the plant which thus 
brushes off on the insect's back (Fig. 239). Then as another flower 
is visited this pollen is brushed off by the stigma thus bringing about 


The summary of the Arthropoda will show under what phylum, 
class and order bees are classified. But here it is necessary to mention 
the following five types of honey bees found in the United States, though 
none are native. 

German, with black-colored abdomen. These are the so-called wild 
honey bees. 

Italian, with yellow-striped abdomen. 

Carniolan, with gray abdomen. 

Cyprian, with yellow abdomen. 

Caucasian, with yellow-gray abdomen. 

All bees are included in the great family Apidae, but there are both 
solitary and social species. Then, too, some are miners, carpenters, leaf- 
cutters, etc. 

As different species of bees have different length of tongues, their 
food must vary accordingly. This was seen in our discussion of the 
bumble bee, which alone of all the bees, has a long enough tongue to 
obtain the nectar from red clover. Short-tongued bees must seek a 
flower with a less deeply placed nectar. 


As flies may carry "tuberculosis, cholera, enteritis (including epi- 
demic dysentery and cholera infantum — the fly-time 'summer complaint' 
of infants), spinal meningitis, bubonic plague, smallpox, leprosy, syphilis, 

The Honey Bee and the Fly 


gonorrhea, ophthalmia, and the eggs of tapeworms, hookworm, and a 
number of other parasitic worms," they are certainly worthy of our 
attention, and should be considered here, although it must not be thought 
that flies are the only carriers of these diseases. It is especially inter- 
esting to know that, while only about two persons die each year in the 
United States from the bites of poisonous snakes and about one hundred 
from the bites of rabid dogs, nearly 100,000 die annually from diseases 
carried by flies. 

There are more than 43,000 different kinds of flies, gnats and mos- 
quitoes which have been described in entomological literature, and there 
is no telling how many more are still unknown. Tachina flies (Fi°-. 
240), already described as killing grasshoppers, and Syrphus flies 
( ) which feed on insects are of real value to man, 

but nearly all others should be exterminated. 1 Over ninety per cent of 
the flies found in and about homes are the regular typhoid flies. When 

Fig. 240. 

The Friend of Farmers. Red-tailed tachina-fly (Winthemia 4-pustulata.) a., 
natural size; b., much enlarged; c, army worm on which fly has laid eggs, natural 
size; d., same, much enlarged. (After S. Singerland.) 

it is remembered that the feet of these are furnished with claws for 
climbing over rough surfaces as well as with two pads, the pulvilli, 
covered with sticky, tubular hairs by which the animal can attach itself 
to ceilings and glass surfaces, one can understand the excellent summing 
up of what this means — that "No more effective mechanisms for col- 
lecting dust could be designed than a fly's feet and proboscis (Fig. 216), 

*In the early part of 1923 hundreds of thousands of dollars were lost in the Santa Clara Valley. 
California, by the larvae of Syrphus flies which could not be washed off the spinach leaves, thus 
necessitating the closing of the canneries. Even friendly insects sometimes do much damage. 


General Biology 

a combination of six feather dusters and thirteen damp sponges. While 
the constant 'cleaning' movements of flies are clearly designed to rub 
off and scatter the adhering germs everywhere they go." 

There are "little house flies" (Fannia canicularis) which probably 
most people believe grow into the regular house flies. Their breeding 
habits and feeding places are quite similar to house flies, but, as flies 
hatch in the adult form they do not grow after once becoming flies. 

Other flies, such as bluebottles, greenbottles, and flesh flies or blow- 
flies, are also found about the home and frequently lay their eggs on 
meat. These flies are scavengers. 

In the south there is the screw-worm fly (Chrysomyia macellaria) 
which deposits its eggs on wounds, for the maggots of this species feed 
on living flesh. It is these flies also which are likely to lay their eggs 
in the nostrils and ears of children or even of adults as they sleep out of 

\ - 

|A ^M 



m /r^T. 









- - 

I J%£ : : 


f||| \ 


f- " ^^ 








■■■■■■ ....-, 

■ ■ . ■ 

<** if?:. - '■, . 

■• - ■'•■'■.. 

- i -fit f 


" f: i 






Fig. 241. 

I. Typhoid fever or house-fly (Musca domestica). a, Adult male; b., pro- 
boscis and palpus of same; c, terminal joints of antennae; d., head of female; e., 
puparium; /.. anterior spiracle; all enlarged. (Howard and Marlatt, Bull. U. S. 
Dept. of Agriculture, 1896.) 

II. Metamorphosis of Saw-Fly. 

III. Tsetse fly, which causes a disease of cattle in Africa, enlarged. (L. 
O. Howard.) 

IV. Larvae of bot flies attached to the walls of the stomach of a horse. (.After 

The Honey Bee and the Fly 371 

doors. The maggots then cause intense pain as they feed on the sur- 
rounding flesh. 

The stable fly (Stomoxys calcitrans) looks something like a housefly 
except that it has a strong piercing beak and sucks blood from animals. 
It is also supposed to be the insect which carries the germs of infantile 

The smaller horn fly (Haematobia serrata) swarms about the bases 
of the horns of cattle, biting constantly. 


Flies (Fig. 241) breed about filth and decaying matter though they 
can and do breed in any wet fermenting vegetable or animal matter. 
The maggots are hard to kill ; they will live in pure kerosene for over 
an hour and even more than thirty minutes in alcohol. They have 
even been bred from the open boxes of snuff on a druggist's counter, 
though tobacco is supposed to be quite injurious to insects. 

After the housefly's eggs are laid, it takes about eight hours for thern 
to hatch into* maggots. These finish their growth in six to seven days, 
burrowing into the ground "under the manure pile" (hence the need of 
concrete floors) and transform into brown puparia, from which they 
emerge as adult flies in three days. 

Hodge and Dawson have summed up the rapid increase in flies most 
tellingly in the following words : "After coming out as adults, they fly 
about over an area not generally more than one thousand yards in 
diameter, and feed and drink from two hundred to three hundred times 
a day for from ten to fourteen days before maturing their first batch of 
eggs. This actually delivers the enemy into our hands. It means that, 
with flytraps on every garbage can and swill barrel, and with everything 
most attractive to flies very carefully kept in these receptacles, not a 
single fly will succeed in feeding for two weeks without getting caught. 
In this case no more eggs will be laid, and the pests will vanish. 

"Allowing ten days of feeding between emergence and oviposition, 
figuring that a fly lays 150 eggs at a batch and lives to lay six batches, 
compute the increase of a pair of flies beginning to lay May 1. Half 
the progeny are supposed to be females. Test the following figures : 

May 10 . . 152 flies. 

May 20 302 flies. 

May 30 11,702 flies. 

June 10 34,302 flies. 

June 20 911,952 flies. 

June 30 6,484,700 flies. 

July 10 72,280,800 flies. 

July 20 325,633,300 flies. 

July 30 5,746,670,500 flies. 

372 General Biology 

"As this last amount makes 143,675 bushels of flies resulting from 
a single pair of flies in three months, one can estimate what the result 
will be if allowed to breed unrestrained during August and September 

"The common sense question, then, is, why not let this pair of flies 
catch themselves in May? This rapid increase also means that anything 
short of extermination is hardly worth the effort. A fly is possessed of 
no more cunning than shot rolling down a board, and the last pair will 
run into a trap as easily as the first. Why not let them all catch them- 

During the winter, especially in cold climes, most of the flies are 
killed, but probably some maggots pass the winter underground and in 
stables where it is sufficiently warm, coming forth in the spring when 
the weather warms up. 

It has often been assumed that burying debris of various kinds 
would kill the maggots. This is not true as the maggots have crawled 
up through six feet of earth with which they were covered. 

The best method of handling debris, such as manure, is to spread it 
on the land daily. This is especially valuable, as manure loses almost 
half its fertilizing power if stored. The sun will dry it and this will also 
prevent the moisture which maggots need in order to thrive. However, 
if this cannot be done, then a solution of iron sulphate (copperas), two 
pounds to the gallon of water, may be thrown over such matter. 
Chloride of lime is expensive and the fumes (chlorine) are likely to in- 
jure the farm animals. 


The Kansas Board of Health Bulletin gives the following methods 
of killing flies : 

"A cheap and perfectly reliable fly poison, one which is not danger- 
ous to human life, is bichromate of potash in solution. Dissolve one 
dram, which can be bought at any drug store, in two ounces of water, 
and add a little sugar. Put some of this solution in shallow dishes and 
distribute them about the house." 

"One of the best fly killers that can be used in the home is a tea- 
spoonful of formalin in a quarter of a pint of water. When this is 
exposed in a room it will be sufficient to kill all flies. They seem to 
be fond of the water. Care should be taken to place it beyond the 
reach of children." 

"To quickly clean a room where there are many flies, burn 
pyrethrum powder. This stupefies the flies, when they may be swept 
up and burned." 

And the Agricultural Extension Department of the International 
Harvester Company suggests the following ointments and sprays to 
keep flies away from cattle : 

The Honey Bee and the Fly 


(Any of the following must be applied frequently, as few will keep 
flies away for more than a day or two following their application.) 

One pound rancid lard, one-half pint kerosene. 

Mix until a creamy mass forms. Best applied with cloth or with 
bare hand. Rub thinly over the backs of the cows. 



Wf^"- : 


I. Ichneumon-fly. Natural size. 

II. Thalessa boring in an ash tree to deposit its eggs in the 
burrow of a horntail larva, a wood borer. From photograph, 
natural size. (After Davison.) 

III. Corn root aphis (Aphis maidiradicis ) , winged and wing- 
less female. The two black processes at the rear are Cornicles. 
(From Needham's "General Biology" bv permission The Comstock 
Pub. Co.) 

374 General Biology 

Three parts fish oil, one part kerosene. Apply with small spray 

Two parts crude cottonseed oil or fish oil, one pint pine tar. Apply 
with large paint brush. 


Many kinds of insects live parasitically for part of their lives, and 
many live as parasites for their whole life. The true sucking lice and 
the bird lice live as external parasites on the bodies of their host through- 
out their entire lives, but they are not fixed — that is, they retain their 
legs and power of locomotion, although they have lost their wings 
through degeneration. The lice deposit their eggs on the hair of the 
mammal or bird that serves as host. The young hatch and immediately 
begin life as parasites, either sucking the blood or feeding on the hair 
and feathers of the host. There are several families of the order 
Hymenoptera, all of whose members live as parasites during their larval 
stage. These hymenopterous parasites are called ichneumon ( ) 

flies. (Fig. 242.) The ichneumon flies are parasites on other insects, 
especially of the larvae of beetles, moths, and butterflies. According 
to Ealand, "the ichneumon flies do more to keep in check the increase 
of injurious and destructive caterpillars than do all our artificial remedies 
for these pests. The adult ichneumon fly is four-winged and lives an 
active, independent life. It lays its eggs either in or on or near some 
caterpillar or beetle grub, and the young ichneumon, when hatched, 
burrows into the body of its host, feeding on its tissues, but not attack- 
ing such organs as the heart and nervous ganglia, whose injury might 
mean immediate death to the host. The caterpillar lives with the ichneu- 
mon grub within it, usually until nearly time for its pupation. In many 
instances, indeed, it pupates with the parasite still feeding within its 
body, but it never comes to maturity. The larval ichneumon fly pupates 
either within the body of its host or in a tiny silken cocoon outside of 
its body. From the cocoons the adult winged ichneumon flies emerge, 
and after mating find another host on whose body to lay their eggs." 

As an example of a parasite living upon another parasite, though 
one of these uses a tree as its host, the remarkable ichneumon fly 
Thalessa (Fig. 242) is an excellent example. This animal, which has a 
very long, slender, flexible ovipositor, finds a spot in a tree where the 
insect Tremex columba ( ), commonly called the 

pigeon horntail, has deposited its eggs about a half inch below the sur- 
face of a growing tree. When these eggs are converted into larva, the 
larva digs still deeper into the tree, filling up the open space behind it 
with tiny chips. Through a very extraordinary instinct the Thalessa 
finds the spot opposite where the Tremex larva lies and "elevating her 
long ovipositor in a loop over her back, with its tip on the bark of the 
tree, she makes a derrick out of her body and proceeds with great skill 

The Honey Bee and the Fly 375 

and precision to drill a hole into the tree. When the Tremex burrow is 
reached, she deposits an egg in it. The larva that hatches from this egg 
creeps along this burrow until it reaches its victim, and then fastens 
itself to the horntail larva which it destroys by sucking its blood. The 
larva of Thalessa, when full grown, changes to a pupa within the bur- 
row of its host, and the adult gnaws a hole out through the bark if it 
does not find the hole already made by the tremex." 

Practically all the mites ( ) and ticks ( ), 

animals closely allied to the spiders, live parasitically. 

Truly Dean Swift was right when he said : 
"Great fleas have little fleas 

Upon their backs to bite 'em, 
And little fleas have lesser fleas, 
And so ad infinitum." 


Sanderson and Jackson's "Elementary Entomology." 

J. Arthur Thomson, "Outlines of Zoology." 

Linville and Kelly, "A Text-book in General Zoology." 

Leland O. Howard, "The Insect Book." 

Vernon L. Kellogg, "American Insects." 

Robert W. Hegner, "College Zoology." 

J. H. Comstock, "Insect Life." 

J. H. and A. B. Comstock, "A Manual for the Study of Insects." 

A. S. Pearse, "General Zoology." 

C. A. Ealand, "Insects and Man." 

E. Dwight Sanderson, "Insect Pests of Farm, Garden and Orchard." 

L. S. and M. C. Daugherty, "Principles of Economic Zoology." 

Joseph Lane Hancock, "Nature Sketches in Temperate America." 

Riley and Johannsen, "Handbook of Medical Entomology." 

Jordan and Kellogg, "Animal Life." 

Jordan and Kellogg, "Evolution and Animal Life." 

Riley, "Destructive Locusts." U. S. Department of Agriculture, 
Bulletin No. 25, 1891. 

C. F. Hodge and S. Dawson, "Civic Biology." 

James A. Nelson, "The Embryology of the Honey Bee." 

Royal N. Chapman, "Animal Ecology with Special Reference to' 

H. T. Fernald, "Applied Entomology." 

J. W. Folsom, "Entomology, with Special Reference to Its Biologi- 
cal and Economic Aspects." 

Augustus D. Imms, "General Textbook of Entomology." 

Arthur S. Pearse, "Animal Ecology." 

H. J. Van Cleave, "Invertebrate Zoology." 

Charles M. Wenyon, "Protozoology, a Manual for Medical Men, 
Veterinarians, and Zoologists." 



IT is generally conceded that those who have been with a business 
organization throughout its growth period know most about that 
business. Such men not only understand a thousand details of the 
work that others do not, but they have definite reasons for their actions 
and policies. The same truth holds good in science. But as none of us 
were present when science began, the only way we can obtain such an 
understanding is to read the story of those who were present ; as a con- 
sequence, the history of any branch of science becomes an important 
study in the college curriculum. 

In reading history we are always inclined to pass some kind of 
judgment on the characters there found. This judgment is, however, 
quite likely to prove erroneous, unless we first know something of the 
times in which they lived, the obstacles they had to overcome, and the 
reasons they had for beginning work in new fields. 

We must weigh the evidence on all sides of a question very care- 
fully, so as not to confuse conspicuousness with importance. For exam- 
ple, an inventor is likely to be widely known because men at large can 
see, use, and understand his invention ; but, as soon as another inventor 
improves, or brings about another apparatus which takes the place of the 
first invention, the first inventor ceases to interest men, and is soon 

Such a lack of consideration does not apply to the real scientist — 
the discoverer of a new principle — for, every invention and every appli- 
cation which his principle brings about in future time, proves that 
principle to be just so much the more important, and causes the scientist 
to be held in greater and greater esteem through onflowing years. 

It is, therefore, the real scientists, the true originators and discov- 
erers of principles, who must be known and honored. 

First, then, let us try to catch a glimpse of the times in which men 
of past ages worked. 

From the very earliest period of which we possess records, men 
have been interested in agriculture and medicine — which means, botany 
and zoology. Botany, in so far as a practical knowledge of food-plants 
was essential to successful agriculture, and in so far as a practical 
knowledge of medicinal plants was essential for the health of man and 
his animal servants. Zoology, in so far as a practical knowledge of the 
breeding of cattle and sheep was essential to a successful livelihood, 

The History of Biology 377 

and in so far as a knowledge of the human body was essential to prevent 
wounded men from bleeding to death. 

Aristotle (384-322 B. C), who was the pupil of Plato, was one of 
the first men to think of botany and zoology as definite branches of 
study. His great contribution to Biology was the discovery of the fact 
that nature worked by definite fixed laws — what we now call the law 
of continuity. 

This discovery is intensely important because it made experimental 
science possible. There would be but little use in spending months and 
years in attempting to prove anything, if the laws of nature worked 
differently at different times, under the same conditions ; for, the real 
value of experimenting is found in one's ability to> prophesy that the 
same result will always take place if the same experiment is performed 
under the same conditions. 

The first mark of a true scientist is accurate observation and perfect 
description, and the second is the power of visualization, by which he 
can build up and mold his interpretations into a principle. 

Aristotle had a mind of the highest type, and so his generalizations 
still hold good after a lapse of thousands of years, provided, always, that 
his facts were correct. He did not have the instruments for accurate 
observation that we now have, so he often had to take for granted many 
things which have since been proved erroneous. But, his logic never 
failed him when his facts were right. 

Theophrastus (370-286 B. C.) laid the foundations of botany. The 
astounding point that meets one in the reading of these old philosophers 
is that they were able to work out so great an amount of detail with 
the poor equipment they had, when we, with all our modern improved 
apparatus, must search most diligently before we can accomplish the 
same results. 

As medical men were the first workers in Biology proper, 
Hippocrates (460-370 B. C.) the father of medicine, must be mentioned. 
He made medicine a separate science and set forth the ideals of the 
medical man which are still an inspiration to all. 

Dioscorides (about 64 A. D.), an army surgeon under Nero, and 
Galen (131-201 A. D.), physician to Marcus Aurelius and his son Corn- 
modus, were both Greek physicians. The former originated the pharma- 
copoeia, which was the standard textbook of botany for some fifteen, 
centuries. The latter wrote an anatomy and physiology which also was 
a standard textbook for medical students for the same length of time. 

Pliny the Elder (23-79 A. D.) wrote a book which, although sup- 
posed to be accurate, had fact and fancy blended to so considerable an 
extent that it is hard to separate them. 

The men mentioned above are the only biological workers of whom 
we have any record up to the time Christianity began to function. 

The Roman Empire was mistress of the world at this time, and 

378 General Biology 

pleasure was the Roman ideal. Christianity strenuously opposed such 
an ideal, and soon won Emperor and people to its side. The moment 
this occurred, all efforts on the part of both student and soldier were 
directed toward performing such acts as would bring glory to the God 
they had accepted. And, as always, when the ideal of a nation is thrown 
aside, the pendulum swings completely over to the other side. Conse- 
quently, after Christianity was adopted, suffering, from having been 
considered a burden and a nuisance to men who held pleasure as their 
ideal, became something to be endured and practically enjoyed, inasmuch 
as he who suffered was thus imitating in some small measure the suffer- 
ings of the founder of Christianity. It follows that no great impetus 
was given to work that had for its object the relief of physical discom- 
forts. At this time, also, barbarian hordes were a constant menace, 
and wars and rumors of wars not only kept men in the field, but forced 
all energy to be directed toward setting up some kind of military and 
defensive stability. And, while many scientific applications are produced 
for destructive purposes in war, there can be no true science at such 
time. Little serious studious work can be accomplished unless there is 
leisure and freedom from danger. 

At this time there were only two fields of work in which a youth 
of ambition might enter — the army and the Church. The first attracted 
men who sought physical power, while the second attracted those who 
sought knowledge. 

The Church, therefore, established universities and libraries in the 
monasteries — the only place where one could find men interested in 
learning. It was here that the works of the great writers of antiquity 
were preserved and used during the times when wars were not being 

Even during these trying times some of the monks compiled animal 
stories which were, however, concerned principally with pointing out 
a moral. Such stories were collected in book form and became known 
as the Physiologus. The physiologus in turn developed into another 
book of similar import called the Bestiaries, while on the botanical side 
a book, which may be compared with the bestiaries, was the Hortus 

Later, another botanical work appeared, called the Herbals. 

In the thirteenth century, Europe became somewhat settled. There 
was then sufficient leisure and safety to permit men to lead studious 
lives. The fame of the great scholars of that day spread rapidly. Every- 
where studious men sought whatever books they could find, and read 
them. Printing had not yet been invented, so it was only in the monas- 
tery libraries that books (written by hand) could be found. These were 
read with avidity, and much which had lain neglected during centuries 
of war and turmoil now was made known to the new generation. This 

The History of Biology 379 

period from about 1250 to 1500 is, therefore, called the Renaissance or 
period of re-birth. 

During the thirteenth century, the Dominican Monk, Albertus 
Magnus (1193-1280), began working on physical experiments, while the 
Dominican, Thomas Aquinas (1225-1274), began to collect and coordi- 
nate all the scientific and philosophical knowledge of his day. 

Following these came the Franciscan Monk, Roger Bacon (1214- 
1294), the real father of modern science. Among his many writings 
we find the first clear and unmistakable statements from which our 
knowledge of modern lenses date. His work is like a modern mono- 
graph in that it gives recognition to the opinions of others. 

The old Romans had, it is true, used pieces of glass with water in 
between for magnifying purposes, but it was Bacon who set men on 
the right path regarding true observation, description, and the use of 
modern laboratory instruments. 

Gesner (1516-1565) wrote his Historia Animalium in several vol- 
umes between 1551 and 1587, which was widely read, although he had 
but little influence on successive generations. 

The next truly great name in the history of Biology is that of 
Vesalius (1514-1564). He wrote the De Humani Corporis Fabrica in 
1543. Up to this time the surgeon would not soil his hands by touching 
and cutting the body. Such work was left for barbers, who performed 
their dissections and operations under the direction of the surgeon. 
Vesalius dissected with his own hands, and then described and pictured 
what he found. Vesalius' old master, Jacobus Sylvius, was a strenuous 
opponent of his pupil, as was also Vesalius' own pupil, Columbus. How- 
ever, another pupil of Vesalius, who later became his successor at the 
University of Padua, was Fallopius (1523-1562), who built upon the 
work of his master. 

Harvey (1578-1657) in 1628 published his Exceircitatio Anatomica 
de Motu Cordis et Sanguinis in Animalibus, in which he showed con- 
clusively that the blood flows in a circle from the heart through the 
blood-vessels and back again to the heart. 

In about 1600, compound microscopes were invented, and it is from 
this time forward that the great microscopical discoveries were made, 
which have changed our modern conception of many ancient problems. 

Robert Hooke (1635-1703) wrote his Micrographia in 1665, in which 
he called attention to the "little boxes or cells" of which plants are 
composed. It is he, therefore, who gave us our first notion of the cell. 

The next important name is that of Van Leeuwenhoek (1632-1723) 
who first saw bacteria, infusoria, yeast, rotifers, hydra, and a host of 
other organisms which were totally unknown up to his time. His work, 
which attracted most attention in the scientific world, however, was his 
description of spermatozoa. His imagination carried him away, for he 

380 General Biology 

was sure he saw definitely-formed tiny human beings in the spermatozoa. 
A great conflict was waged by those who agreed with him and his 
school, who were known as spermists, insisting that it was the sperm 
that was the all important factor in producing life, and the opposing 
school known as ovists which insisted that it was the egg and not the 
spermatozoa which developed into new offspring. 

Swammerdam (1637-1680), in his Biblia Naturae, compiled long and 
painstaking accounts of his researches on the anatomy of insects. Up 
to his time, insects were considered only unorganized physical masses. 

Malpighi (1628-1694) of Bologna worked on plants and animals. 
He made elaborate studies and illustrated them, on the development of 
the plant-embryo, as well as on the embryology of the chick, the 
anatomy of the silk-worm, and the structure of glands. 

Chronologically, the systematists should be mentioned at this point, 
but logically, it is better to introduce the student to the whole subject 
of classification and the men who did the classifying at the same time. 
Therefore, this subject will be treated in the next chapter. 

As soon as there is any considerable classification and description 
of a subject, men begin to divide that subject into individual parts or 
units so that workers may narrow their field and confine their work to 
such a limited group or unit. 

Comparative anatomy, physiology, histology, embryology, genetics, 
and organic evolution, are the main divisions into which Biology is thus 

The work done by first-year students of Biology, as set forth in 
this book, consists of studying a type-form of the principal phyla of 
plants and animals, and then attempting to develop biological principles 
from the knowledge thus gained. This first-year work, therefore, in- 
cludes the fundamentals of botany and zoology. The third semester's 
work is confined to the specialized study of embryology, and the fourth 
semester's work is comparative anatomy and physiology. In this last 
semester's work the student studies in detail each organ or organ-system 
of the great divisions of zoology and then compares these, system by 

Probably the first man to attempt this latter method was Severinus 
(1580-1656) of Naples. In 1645 he published a volume suggesting that 
all vertebrates and man had much in common, structurally. However, 
over a century before this time, Belon had made drawings of the skel- 
etons of birds and man and placed them side by side so that differences 
and similarities could be noted. Then came Tyson (1650-1708) of Cam- 
bridge, who is the father of our modern method of treating comparative 
findings in monograph form. His work was a comparison of man and 

Cuvier (1769-1832) of Paris is, however, the first of the great men 
in this field of work. He was the first to embrace both living and extinct 

The History of Biology 381 

forms in his comparisons, and he also obtained a wider grasp of the 
problem confronting him than any of his predecessors. A good illustra- 
tion of the synthesis sought for, and the breadth of knowledge desired 
in this department of research, can be found in his famous statement, 
"Give me a tooth, and I will construct the whole animal." 

This is the keynote to comparative study. It means that every 
change in function modifies a structure, and that, if we can know thor- 
oughly all there can be known about function and its effect on structure, 
and every change in one structure which may change a related structure, 
we can tell what the functions must have been, in a given structure, 
and vice versa. 

There are men who were lesser lights in the field of comparative 
anatomy even before Cuvier's time, whose names it is well to know : 
John Hunter (1728-1793), who founded the Hunterian Collection in 
England; Camper (1722-1789) of Groningen, and Vicq d'Azyr (1748- 
1794) in Paris. All of these did synthetic work, but their breadth of 
knowledge, view, and vision fell far short of that of Cuvier. 

Following Cuvier came Milne-Edwards and Lacaze-Duthiers in 
France ; Meckel, Rathke, Johannes Muller, and Gegenbaur in Germany ; 
Owen and Huxley in England ; Aggassiz, Cope, and Marsh in America. 

When men once became interested in the great structural problems 
of zoology it was but natural that others should become interested in 
those that were functional. Here was the birth of modern physiology. 
The medical men were the first to do work in these fields. They estab- 
lished systems of thought known as the iatro-mechanical and iatro- 
chemical schools. 

Haller (1708-1777) took the work of these men, surveyed it, and 
evaluated it, so that he may really be called the father of modern 

The first work in physiology was done on nutrition and respiration. 
Reaumur (1683-1757) of Paris, and the Abbe Spallanzani (1729-1799) 
of Pavia did the most remarkable work in this field, although they had 
forerunners on whose work they built in turn. 

Such forerunners were van Helmont (1577-1644), Sylvius (1614- 
1672), Bishop Stensen (1638-1686), de Graff (1641-1673), Peyer (1653- 
1712), and Brunner (1653-1727). 

The great names in chemistry whose work affected biological 
students are primarily Boyle (1627-1691), Priestly (1732-1804), and 
Lavoisier (1743-1794). 

In physiology proper the greatest names in Germany are : Liebig 
(1803-1873), Wohler (1800-1882), the brothers Weber (E. H., 1795-1878, 
and W. E., 1804-1891), Ludwig (1816-1895), Helmholtz (1821-1894), 
Johannes Muller (1801-1858), and du Bois-Reymond (1818-1896). In 
France, Dumas (1800-1884), Magendie (1783-1889), and in England, 

382 General Biology 

Hall (1790-1857). The greatest of the physiologists is undoubtedly 
Johannes Muller. 

In botanical physiology, Hale (1677-1761), is the greatest, while 
Cesalpino (1519-1603), Jung (1587-1657), and van Helmont (1577-1644), 
occupy high places. 

Ingen-Housz (1730-1799) was the first to show that carbon dioxide 
from the air is broken down in the leaf when the plant receives sunlight, 
and that the carbon is retained and assists materially in nutrition and 

De Saussure (1740-1799) showed further that water and various 
salts from the soil produced the remaining factors in this process, while 
Boussingault (1802-1887) gave us our knowledge of chlorophyl. 

Haller and van Leeuwenhoek were "pre-formationists." They sup- 
posed that each sperm or egg-cell already contained an embryo some- 
what fully formed, and that all that occurred during the growth period 
was an enlarging of the parts which were already present. Such an 
idea meant that every human germ-cell must have every other complete 
human being that could ever descend from it, within itself, fully formed, 
but very small. We know now that both those who held this theory 
and those who opposed it were wrong. There must, of course, be 
present in each germ-cell a potentiality which can develop into what 
it is to become, but this by no means signifies that the embryo possesses 
a definitely formed embryo within it in turn. The new embryo is always 
organized little by little until it becomes the completed individual adult 

However, it is natural to see how and why observers thought they 
saw the complete embryo in the egg. In our study of embryology we 
shall see that when the hen lays an egg, it is already from twenty-two 
to thirty-six hours old, and consequently, even when we have a freshly 
laid egg (provided it is fertile), there is already an embryo which can be 
seen. It was with material of this kind that these men had to work. 

Wolff (1733-1794) had proved that the pre-formationists were in 
error, but Haller, who held the intellectual reins of workers in zoology 
at the time, refused to accept it, and so the lesser lights also refused. 

It was but natural that, after Hooke had observed that plants were 
composed of cells, something should be done with such a finding. 
Brown (1773-1858), working on the cell, discovered the cell nucleus in 
1831, and the botanist Schleiden (1804-1881), and the zoologist Schwann 
(1810-1882) published their works in 1838 and 1839, respectively, show- 
ing that plants are developed from cells, and that plants and animals are 
alike in being composed of cells. 

An important point was made in suggesting that each cell has two 
functions : one to perform the work itself and the other to perform a 
task which makes it an integral part of a larger organism. 

The History of Biology 383 

Schultze (1825-1874) in the early sixties established the idea of pro- 
toplasm as the living substance of all cells. This protoplasm was called 
by Huxley the "physical basis of life." 

In embryology Fabricius (1537-1619) published a paper describing 
the sequences of development in the hen's egg up to the time of hatching. 
Harvey was a pupil of Fabricius, and built upon the work of his master. 
These men opposed the pre-formationists, and called their theory 
epigenesis — which simply means that the embryo arises by a gradual 
differentiation of unformed material in the egg. 

Malpighi in 1672 sent two important papers on embryology to the 
Royal Society, but apparently the time was not yet ripe for his work 
and it was neglected for nearly a century. He stood with the epigenetic 

Bonnet (1720-1793) was one of the important men at this time who 
threw the weight of his influence with Haller toward the pre- 

At present embryologists hold, as was stated above, that there 
really is an organization of some kind in both egg and sperm, but that 
no embryonic shape has yet been established. The definite shape comes 
forth only by the gradual differentiation of the unformed (but not 
unorganized) matter. We may, therefore, say that "the whole future 
organism is potentially and materially implicit in the fertilized egg cell," 
which means that both sides were partially right. 

However, the greatest name in embryology is von Baer (1792-1876). 
His work was done in the thirties of the last century. He is the father 
of comparative embryology. It was he who first noted and described 
cleavage, germ-layers, tissue, and organ differentiation, and gave us the 
well-known "recapitulation theory," now often called Haeckel's "Law of 
Biogenesis," on account of Haeckel's popularization of it. It will be 
remembered that this theory holds that embryos pass through the adult 
stages of the race to which they belong. 

The origin of life has always been an interesting speculative subject 
for thinking men, and many and mysterious are the ways in which life 
was supposed to spring forth spontaneously. Aristotle thought that 
mice developed from the river's mud, while later writers suggested that 
old rags and cheese combined in a dark cellar would produce the same 
result. The history of this subject makes more than fascinating reading. 

Francesco Redi (1626-1698) was probably the first man to demon- 
strate experimentally that life did not spring forth spontaneously as 
commonly supposed. He placed very thin cloth over a dish containing 
decaying meat and found tliLt, when flies were thus prevented from 
coming in contact with the meat, no maggots formed, although maggots 
were always supposed to arise spontaneously from decaying meat. But 
Redi himself found parasites of various kinds within the bodies of other 


General Biology 

Aristotle, 384-322 B. C. 

Francesco Redi, 1626-1697. 

Cuvier, 1769-1832. 



jjj % , 


'-~- ; '' ^* 


Lazzaro Spallanzani, 1729-1799. Johannes Muller, 1801-1858. 

Robt. Brown, 1773-1858. 

Max Schultze, 1825-1874. 

August Weismann, 1834-1914. 

Louis Pasteur, 1822-1895. 
Fig. 243. 
(Aristotle and Max Schultze, from Needham's "General Biology" by permission 
of The Comstock Publishing Co., Publishers. Pasteur, from G. Stuart Gager's 
"Fundamentals of Botany" by permission of P. Blakiston's Sons & Co., Publishers. 
Remaining photographs from Wm. A. Locy's "Biology and Its Makers" by per- 
mission of Henry Holt & Co., Publishers.) 

The History of Biology 385 

animals, and these he could not account for; so his experiment, while a 
classic, did not settle the problem for others any more than it did for 
himself. The settling of this vexed question was left for Louis Pasteur 
(1822-1895), who first showed that decay was not the cause of micro- 
organisms but the result of them. His experiments were made while 
working on fermentation problems, and it is from his work that all 
modern medicine dates, for he was the founder of the science of 

In genetics or inheritance, from a purely biological angle, August 
Weismann's (1834-1914) work, The Germ Plasm, stands out promi- 
nently. It was Weismann who called attention to the fact that the 
bodily characteristics of any individual have but little, if any, effect on 
succeeding generations. He held that germ-plasm alone carries inher- 
itance. In other words, that acquired characteristics are not likely to be 
inherited, and that, if we are to make any change in future generations, 
we must first learn how to make a change in the germ-cells. 

Francis Galton (1822-1911) gathered a great quantity of statistics 
on the stature of parents and children and published the result of his 
research in the eighties. 

The most important name in the study of inheritance is that of the 
Augustinian monk, Johann Gregor Mendel (1822-1884), who combined 
experimental breeding of plants with a thoroughly scientific philosophy, 
and evolved from this combination the Mendelian laws which are now 
used wherever breeding experiments are performed, whether on plants 
or animals. 

In the field of organic evolution, one may find among the ancients 
many thoughts which show conclusively that they were not unaware of 
a gradual change from smaller beginnings to greater and more developed 
products. Thus St. Augustine (died 604) calls attention to the fact 
that a God is the greater, the more potentialities he can enclose within 
a smaller area, which potentialities can then unfold and evolve. 

Among the moderns, Buffon (1707-1778), was the first to obtain a 
clear inkling of geographical isolation, struggle for existence, and arti- 
ficial and natural selection, and he propounded a theory of how varia- 
tions came about through environment. 

Erasmus Darwin (1731-1802) wrote on changes going on in the 
animal world and embodied his ideas in verse. 

Lamarck (1744-1829) is the most philosophical, which means the 
most profound, of all the writers of the evolutionary school, as he 
actually tried to explain WHY changes took place in the organic world. 

Cuvier (1769-1832), who was a contemporary of Lamarck, and who 
at that time held the highest attainable place in the zoological world, 
was a consistent opponent of Lamarck, but Geoffroy Saint-Hilaire (1772- 
1844), though never attaining the rank of Lamarck, was a staunch up- 

386 General Biology 

holder of the Lamarckian principles, and Goethe (1749-1832), the famous 
poet, who was also a famous scientist of his day, became a disciple of 
the new doctrine. 

Lyell (1797-1875), the Englishman, in the early thirties of the last 
century wrote his Principles of Geology which convinced men that the 
same causes now in action always had been, and that we could, therefore, 
by studying the time it took to make present changes in the earth's 
surface, estimate the length of time and the age of the various strata 
of the earth. 

With the intellectual soil prepared in this way, Charles Darwin 
(1809-1882), published his epoch-making book, The Origin of Species 
by Natural Selection, in 1859. Darwin accepted, without explaining, 
the fact that variations do occur. He assumed that the origin of existing 
species could be explained by accepting the fact that variations did 
occur, and that nature then selected the organisms which should con- 
tinue to exist by killing off those which did not inherit as many varia- 
tions of a survival value. He assumed that acquired characteristics were 
inheritable, and that the struggle for existence eliminated the unfit. 
Darwin had spent twenty years in gathering the facts on which he based 
his theory, but Alfred Russel Wallace (1822-1913) had reasoned out a 
similar theory without having the facts that Darwin had, and it is an 
interesting coincidence that both men were working independently on 
the same thought at the same time. Darwin was willing to surrender 
all his work to the younger man, but Wallace insisted that Darwin was 
to have the credit as the latter had done such an immense amount of 
work on the matter. 

Evolution now serves the biological world as a sort of general plan 
of the results of heredity, while genetics deals with the factors which 
produce these results. 

Thomas Huxley (1825-1895), though not a believer in the Darwinian 
theory of natural selection, sprang to the defense of Darwin, primarily, 
as Professor Poulton says, because Darwin was so constantly and per- 
sistently treated unjustly. It was Huxley who made Darwinism popular. 
Hooker (1817-1911) in England, Haeckel (1834-1919) and Weismann 
in Germany, and the botanist Gray (1810-1888) in America, were early 
converts. Haeckel, however, was too much of the showman, and was 
always willing to sacrifice truth and accuracy to win his point. 

Summing up what has been said, we may say that the basis of great- 
ness in science is not the brilliancy of an individual discovery, but the 
finding and enunciating of a principle which can find many applications 
by those who follow. 

The great findings, considered from this point of view of obtaining 
principles which have a wide influence in Biology, may be said to be 
the discovery of protoplasm; the establishment of the cell-theory; the 

The History of Biology 387 

theory of organic evolution ; the demonstration that germs are a tremen- 
dous factor in disease; and the experimental study of inheritance as 
suggested by the work of Mendel and Weismann. 

And the most important writings of the most important men may 
be summarized here by following Professor William Locy's account, 
which we have modified slightly. 


The progress of Biology has been owing to the efforts of men of 
very human qualities, yet each with some special distinguishing feature 
of eminence. Certain of their publications are the mile-stones of the 
way. It may be worth while, therefore, in a brief recapitulation to 
name the books of widest general influence in the progress of Biology. 
Only those publications will be mentioned that have formed the starting 
point of some new movement, or have laid the foundation of some new 

Beginning with the revival of learning, the books of Vesalius, "De 
Corpora Humani Fabrica" (1543), and Harvey, "De motu Cordis et 
Sanguinis" (1628), laid the foundations of scientific method in Biology. 

The pioneer researches of Malpighi on the minute anatomy of plants 
and animals, and on the development of the chick, best represent the 
progress of investigation between Harvey and Linnaeus. The three 
contributions referred to are those on the ''Anatomy of Plants" 
(Anatome Plantarum), (1675-1679) ; on the "Anatomy of the Silkworm" 
(De Bombyce, 1669) ; and on the "Development of the Chick" (De 
Formatione Pulli in Ovo and De Ovo Incubato, both in 1672). 

We then pass to the "Systema Naturae" (twelve editions, 1735- 
1768), of Linnaeus, a work which had wide influence in stimulating 
activity in the systematic study of botany and zoology. 

Wolff's "Theoria Generationis," 1759, and his "De Formatione In- 
testinorum," 1764, especially the latter, were pieces of observation mark- 
ing the highest level of investigation of development prior to that of 
Pander and von Baer. 

Cuvier, in "Le Regne Animal," 1816, applied the principles of com- 
parative anatomy to the entire animal kingdom. 

The publication in 1800 of Bichat's "Traite des Membranes" created 
a new department of anatomy called histology. 

Lamarck's book, "La Philosophic Zoologique," 1809, must have a 
place among the great works of Biology. Its influence was delayed for 
more than fifty years after its publication^ 

The monumental work of von Baer "On Development" (Ueber 
Entwicklungsgeschichte der Thiere), 1828, is an almost ideal combina- 
tion of observation and Conclusion in embryology. 

The "Mikroscopische Untersuchungen," 1839, of Schwann marks 
the foundation of the cell-theory. 


General Biology 

Charles Darwin, 1809-1882. Alfred Russell Wallace, 1823-1913. Thomas Henry Huxley, 


Lamarck, 1744-1829. 

Johann Gregor Mendel, 

Hugo De Vries, 1848- 

M. Schleiden, 1804-1881. 

Theodor Schwann, 1810-1882. 

Karl Ernst von Baer, 

Fig. 244. 
(De Vries and Mendel, from G. Stuart Gager's "Fundamentals of Botany" by 
permission of P. Blakiston's Son & Co., Publishers. Remaining photographs from 
Wm. A. Locy's "Biology and Its Makers" by permission of Henry Holt & Co., 

The History of Biology 389 

The "Handbook" of Johannes Muller (Handbuch der Physiologie 
des Menschen), 1846, remains unsurpassed as to its plan and its 

Max Schultze in his treatise, "Ueber Muskelkoerperchen und das 
was man eine Zelle zu nennen habe," 1861, established one of the most 
important conceptions with which Biology has been enriched, viz : the 
protoplasm doctrine. 

Darw.n's "Origin of Species," 1859, is, from our present outlook, 
the great classic in Biology. 

Pasteur's "Studies on Fermentation," 1876, is typical of the quality 
of his work, though his later investigations on inoculations for the pre- 
vention of hydrophobia and other maladies are of greater importance 
to mankind. 

Mendel's "Versuche iiber Pflanzen-Hybriden" appeared in 1865 in 
a little periodical published in Briinn, Austria, where Mendel was abbot 
of an Augustinian monastery. It remained entirely unknown to the 
scientific world until 1900 when three workers in the natural sciences 
rediscovered it. These men were De Vries, Torrens, and Tschermak. 

Mendel's work has become the foundation upon which all modern 
research along genetic lines is based. Castle says, "Mendel had an ana- 
lytical mind of the first order which enabled him to plan and carry 
through successfully the most original and instructive series of studies 
in heredity ever executed," and Bateson suggests that "had Mendel's 
work come into the hands of Darwin, it is not too much to say that the 
history of development of evolutionary philosophy would have been 
very different from that which we have witnessed." 

Weismann's "The Germ-Plasm, a Theory of Heredity," appeared in 
1893. It demonstrated the "continuity of the germ-plasm," a valuable 
starting point for theorizing upon Mendel's laws. 

De Vries' "Die Mutationstheorie," published in 1901, caused much 
of Darwin's theory, that evolution comes about gradually, to be set 
aside. The sudden springing forth of new forms, rather than a slow 
change requiring thousands of years, won many scientific men to it. 
In fact, all modern evolutionary theories follow either the Darwinian 
or the De Vriesian type, or build new ones on modifications of these. 

It is somewhat puzzling to select a man to represent the study of 
fossil life. One is tempted to name E. D. Cope (1840-1897), whose re- 
searches were conceived on the highest plane. Zittel (1839-1904), how- 
ever, covered the entire field of fossil life, and his "Handbook of Paleon- 
tology" (1876-1893) is designated as a mile-post in the development of 
that science. 

Before the Christian era, the works of Aristotle and Galen should 
be included. 

From the viewpoint suggested, the most notable figures in the de- 
velopment of Biology are : Aristotle, Galen, Vesalius, Harvey, Malpighi, 

390 General Biology 

Linnaeus, Wolff, Cuvier, Bichat, Lamarck, von Baer, J. Miiller, 
Schwann, Schultze, Darwin, Pasteur, Zittel, and Mendel. 

Such a list is, as a matter of course, arbitrary, and can serve no 
useful purpose except that of bringing together into a single group the 
names of the most illustrious founders of biological science. The indi- 
viduals mentioned are not all of the same relative rank, and the list 
should be extended rather than contracted. Schwann, when the entire 
output of the two is considered, would rank lower as a scientific man 
than Koelliker, who is not mentioned, but the former must stand in the 
list on account of his connection with the cell-theory. Virchow, the 
presumptive founder of pathology, is omitted, as are also investigators 
like Koch, whose line of activity has been chiefly medical. 

Henry F. Osborn, "From the Greeks to Darwin." 

L. C. Miall, "History of Biology." 

William C. Locy, "Biology and Its Makers." 

Garrison, "The History of Medicine." 

Albert H. Buck, "The Growth of Medicine from the Earliest Times 
to about 1800." 

Albert H. Buck, "The Dawn of Modern Medicine." 

Lorande L. Woodruff, "History of Biology," in The Scientific 
Monthly, March, 1921. 

A. G. Little, "Roger Bacon. Essays contributed by various writers 
on the occasion of the commemoration of the seventh century of his 
birth." (1914.) 




540 Xenophanes was first to recognize fossils as proving that the 

earth was formed under the sea and rose out of it. 
500 Heraclitus, often called the first evolutionist. He first advanced 

the principle that "all things flow." 
450 Empedocles was first to suggest natural selection and survival of 

the fittest. 
400 Hippocrates is called "the Father of Medicine." 
350 Aristotle, founder of zoology. 
320 Theophrastus, first botanist. 
320 Erasistratus, first to give mechanical explanation of disease 

300 Herophilus, first anatomist. 

A. D. 

79 Pliny wrote the first popular natural history. 
160 Galen founded medical physiology. 
1266 Bacon wrote his Opus Majus. 

The History of Biology 391 

1542 Vesalius, founder of modern anatomy. 

1548 Falloppio, anatomist. 

1551 Gesner gathered the first botanical garden (of fruits and flowers) 

and arranged the first zoological museum. 

1560 Eustachio, anatomist. 

1583 Caesalpinus classified plants by flowers. 

1590 Janssen, J. and Z., discovered the compound microscope. 

1603 Fabricius discovered valves in the veins. 

1603 Harvey discovered circulation of the blood. 

1622 Ascello discovered the lacteals. 

1649 Rudbeck discovered the lymphatics. 

1650 Swammerdam was first great student of insects in relation to 

plants and medicine. 
1661 Malpighi, founder of pathology. He discovered the capillaries in 
the lungs ; founded modern embryology by a study of the incu- 
bation of the chick (1672). 

1667 Leeuwenhoek, first to see bacteria. 

1668 Redi disproved spontaneous generation of insects by the discovery 

of eggs and larvae. He wrote "Esperienze intorno alia Gen- 
erazione degl' Insetti." 

1670 Mayow studied animal respiration. 

1671 Hooke worked out microscopical structure of plants. 

1680 Borelli proved that all the movements of animals are caused by 
muscles pulling on bone levers ; wrote "De Motu Animalium." 

1682 Grew studied structure of plants. 

1693 Ray classified plants. 

1727 Hales investigated respiration of plants. 

1743 Haller, father of modern physiology. 

1744 Reaumur studied insects. 

1749 Buffon wrote a natural history. 

1753 Linnaeus, founder of modern botany; classified plants. 

1761 Koelreuter studied hybridization of plants. 

1764 Bonnet, evolutionist; grouped animals in an ascending series. 

1764 Wolff, Friedrich Caspar, overcame the pre-formation doctrine. 

1772 Rutherford discovered nitrogen. 

1774 Priestley discovered oxygen and studied the breathing of plants. 

1775 Spallanzani disproved spontaneous generation of bacteria and 

molds and demonstrated presence of living germs in the air. 

1789 Galvani discovered animal electricity. 

1790 Goethe worked out a scheme for the metamorphosis of the parts 

of plants. 
1794 Darwin, Erasmus, grandfather of Charles Darwin; wrote "Zoono- 

mia," a long poem outlining evolution of life. 
1796 Jenner discovered vaccination. 
1796 Sprengel studied fertilization of plants. 

392 General Biology 

1800 Cuvier, founder of modern comparative anatomy; wrote "Le 
Regne animal," 1817. 

1800 Bichat, founder of modern histology. 

1801 Lamarck invented a scheme for the evolution of animals (by 

conscious effort and inheritance of acquired characters; not 

1801 Treviranus introduced the name "Biology" as distinguished from 

"botany," "zoology," "physiology," "anatomy," etc. 
1804 Humboldt studied distribution of plants. 
1807 Rumford, Count, demonstrated absorption of carbonic acid by 

1811 Bell, Charles, discovered motor and sensory nerve roots; founder 

of modern neurology. 
1818 G. St. Hilaire pointed out unity of plan in animals. 
1823 Von Baer discovered the law of embryological development; (all 

higher forms pass through somewhat similar forms to lower 

ones in the embryological period). 
1830 Brown described cell nucleus. 
1833 Miiller, Johannes, founder of modern comparative physiology. 

Wrote Handbuch der Physiologie des Menschen. 
1835 Dujardin studied protoplasm. 
1838 Schleiden discovered the cell as unit of structure in plants. 

1838 Schwann discovered the cell as unit of structure in animals. 

1839 Agassiz wrote on fresh-water fishes. 

1841 Helmholtz discovered rate of nerve impulse. 

1853 Mohl studied protoplasm (living substance). 

1857 Pasteur, founder of bacteriology; studied fermentation. 

1858 Darwin reported his work upon the origin of species by natural 

selection and applied evolution to man. 

1858 Wallace reported his work upon the origin of species by natural 

1858 Virchow worked out cellular pathology; founder of modern cellu- 
lar pathology. 

1861 Schultze, Max, established protoplasm doctrine. 

1863 Huxley wrote "Evidence as to Man's Place in Nature." 

1863 Lyell wrote "The Antiquity of Man." 

1865 Sachs studied structural botany. 

1865 Mendel, founder of modern genetics; discovered the law of 

1867 Lister worked out aseptic surgery. 

1875 Galton studied inheritance. 

1875 Hertwig, O., studied fertilization. 

1880 Koch proved the relation of bacteria to disease. 

1880 Laveran discovered malarial parasite (in the mosquito). 

The History of Biology 393 

1886 Leuckart settled the modern classification of animals ; specialized 
on parasites. 

1893 Weismann showed that germ-plasm and somatoplasm are distinct. 

1893 Zittel wrote most important work on fossils. 

1888 Finlay ^ discovered the relation 

1898 Reed [-between yellow fever 

1898 Lazear J and the mosquito. 

1898 Howard discovered relation between typhoid fever and the house 

1900 De Vries, Correns and Tschermak, all working independently, re- 
discovered Mendel's law of heredity. 

1903 Stiles discovered hookworm in the United States. 

1914 Goddard proved feeble-mindedness a unit character. 

1915 Stockard discovered influence of alcohol on offspring. ■ 


L. C. Miall, "History of Biology." 
Baas, "Outlines of the History of Medicine." 
Garrison, "History of Medicine." 
Hodge and Dawson, "Civic Biology." 
Batesen, "Mendel's Principles of Heredity." 
William A. Locy, "Biology and Its Makers." 
William A. Locy, "The Main Currents of Zoology." 
William A. Locy, "The Growth of Biology." 
Erik Nordenskiold, "Die Geschichte der Biologic" 



JUST as we attempt to read and interpret the history of man's 
progress in the handicrafts, through the remnants of tools and 
pottery which are found in various parts of the world, so we attempt 
to read and interpret the changing conditions which have taken place 
in the earth's crust by the study of geological and paleontological find- 
ings. Geology concerns itself with the changes in the earth itself, while 
paleontology seeks to build up a meaningful account of the changes 
which may have taken place in living organisms throughout the past, 
as demonstrated by their fossil remains (Fig. 245). 

There are two general ways in which layers of rock and soil have 
been laid down. The first has come about by the formation within the 
earth of great masses of molten substance which was then thrown out 
by volcanic action. Such masses harden to form minerals and other 
heat products. If the minerals then become concentrated, they are called 
ores. All such products formed by heat are known as igneous forma- 

The second way in which changes have come about is this : Various 
horizontal soil-layers have been shifted about by climatic changes such 
as a subsiding of land surfaces and an elevation of the edges of the 
ocean. This causes the lowered continent to be covered by shallow 
water, and later, when this condition is again reversed, a layer of sedi- 
ment is left behind. It is in this sediment that millions of marine-forms 
of life are stranded. If the sediment hardens, and these marine organ- 
isms are safely protected from air and superficial decay, their bodies 
will be preserved as fossil remains. 

Fossil remains are, therefore, observed most frequently in the 
deposits on the floors of lakes, in peat-marshes, in the deltas of river- 
mouths, and under the stalagmites in caverns in limestone districts. 

The exceptional conditions necessary to preserve organic forms will 
rarely be found everywhere, so that we must remember that no matter 
how many fossil remains may be found, only a very infinitesimal portion 
of the living forms of any given period will become known to us. Then, 
too, in those which are preserved, most, if not all, of the softer parts of 
the organism are destroyed, only the hard portions remaining. 

The necessity for coordinating the facts found in many and varying 
ways is of prime importance in the science of paleontology, for without 
such coordination there is neither sense nor value in its study. This 
will be demonstrated quite clearly in what follows. 



Geology and climatology attempt to explain each other, the former 
by its effect upon climate, and the latter by its effect on the changing 
strata which go to make up the earth's surface. In fact, it is the 


IJ.00O tO 150.000 YEARS 



z to^ 

Age 6t n&rv, Insects and all 
those Mammals now living; 
All Phyla of Plants includ- 
ing highest flowering 

Quartern*™ or Pleistocene 
(pieistos.nojttiuinot- recent") 
OUcial Period Also 
Called Metal »ge of 
Palaeolithic <s<3es 

Tapir - , Pecary, Bison, Llama, Equus, 
Megatherium, rlylodorv 

(Gigantic sloths) (Oigantic sloths) 

All trace of Man lost 
Mammals abundant, m^ny 
of which are now extinct 
(PitheK0S = ape+ anthropos= 
rlan) Found in Java _, 
Probably at close or 
Pliocene Period 

f-C- O 



E(JUUS Bed5 (Equus Horse) 

Equus, Tapirus.Elephas 

Pliohippus Beds Hippus = Hoi'se 
Pliohippus, Mas to den, Bos., etc 

Drimntes Had made great 
Progress. Ancestral 
Stock of gibbons 
Dryopithecus (Orus-Trw* 
Large Anthropoids 
Increase in higher 
flowering Plants 


Miohippus Beds ,_. . 

Miohiopus, Oiceratherium&hornedjJlMnohyus. 
Oreodon Beds.(orae-nou * ir.»odont.Too+h) 

Edendates. Hyoenodon, Hyrocoden. 
BrontothClium Beds. (Bron+e-ThunderVTherion- Beast) 

Mesohippus, Kenodus, Elothci'ium 

Mammalian Forms 

abundant Many now 


Increase in "lowering - 

Plants 5 



Diplacodon Beds Epihippus. Amynodon. 
Oinocerus Beds. Tinoceras, Uintatheiium 

Limnonyus, Orohippus,Helal?tes Colonoceras. 
Coiyphodon Beds. Eohippus, tlonKeys, 

(CorUphe -- Summit + odont. Tooth 

Qrni vores. Ungulates, Til/odon+s. Rodents. 



Bird like Reptiles 
Flying Reptiles 
Toothed Birds" 
First SnaKes. 
Bony Fishes abound; 
SharKs numerous, 

Rapid increase 
of Lower Flowering 


nJ -Si, 

Lignite Series 
Hydrasaurus, Drypfosaui'us 

Ptei'ai\0d0n BedS.(PterodaduS-winc<ed reptile <- 
anodon- Toothless) 

Birds with Teeth, Hesperornis. 
Ichthyornis, Mosasaurs 
Pterodacfhyls. P/esiojaurs. 

DaKora (fi'oup 

First Birds, 
Giant Reptiles. 
Clams and Snails 


Ferns , Cycads, 
and Coniters. 

e=S>- o 

Atlantasaums Beds 
Dinosaurs, Apcxtosaurus. 
Nanosaurus, Turtles, DiplosauruS. 

First Mammal Found, 
(a Marsupial); 
sharks reduced to 
new Forms, 
Bony Fishes appeal' 

Ferns, eveads, 
and Conifers. 

1 S 

Conn<?ct»cuf River bods. 
Dinosaur Foot-prints. (Amphisaurus) 

Crocodiles, (Bclodon). 

Fig. 245. 

Composite Palaeontological Chart, compiled from many authors, showing geo- 
logical strata and fossil-forms found in each. It will be noted that the number of 
years assigned each stratum varies from any given amount to ten and even a 
hundred times that number. The student must therefore realize that all such 
estimates are only guesses. What he must know is the relative percentage of 
time and the relative percentage of depth of each layer and speak only in terras 
of "eras" and depths. 

Professor Osborn has just described (Natural History, for November-Decem- 
ber. 1921) a Tertiary man living long before the ice-age. 


General Biology 


changing climatic conditions which give us the terms "ages 
"periods," such as the carboniferous age and the glacial period. 

If the deposition of the earth's layers has been laid down by water 
and air, the various strata show such causes by forming a coarse sand- 
layer, followed by a layer of finer sand or mud. Or, two sandy layers 
will be found separated by thin layers of muddy shale, the exact forma- 
tion depending upon the velocity of both sand and water. 

Or, there may be mechanical and chemical changes which produce 
beds of rock sand or gypsum between beds of marl. Likewise, organic 



*\ ° "» 

(O (jj tz> 


£ O0-- 






E&rliest of true 



Lung Fishes; 

Fringe Fins; 

First Cray Fishes. 

Insects abundant; 


Fresh Water Mussels. 






First Amphibians. 
(FrogliKe Animals) 
First Long Shells 

HollirtKs abundant 

First Crabs 

First truly 
terrestrial or air- 
breathing animals; 
First Insects, 
Corals abundant , 
Mailed Fishes 
Probably some 
Land Vegetation 

First Known Fishes: 
(Fishes having no jaw*. 
Segmented Backbones or 
Limbarches & Forepart 
protected by bony Plates 
Cartilaginous Skeleton ; 
Brachiopods , 

Invertebrates only. 
Probably some 
Higher Algae 





Red Sandstone, etc 
riagnesian Limestone 

Coal Measures. 
First Reptiles(?) 


Carboniferous Limestone 


Schoharie Grit 

Some Limestone 

Slates, Sandstones, 
Volcanic KocKs, etc. 

Slates Sandstones, etc 


o <v 

T 00_e< 

Simple Marine 

Probably very 
simple Algae 

Slates, Volcanic Rocks, etc 
No Vertebrates Known 

Fig. 245. 

Paleontology 397 

activities may have their influence as shown by the fine beds of coal 
succeeding layers of sand, or by a layer of large fossils imbedded in 

As there is a tremendous pressure of the superincumbent layers 
upon the underlying strata, the lower layers as well as their fossil con- 
tents are often crushed and injured. Extreme care must, therefore, be 
taken to interpret one's findings. One can readily grasp what such 
pressure would accomplish in the delicate layers of shale (called paper- 
shales), which range from sheets as thin as paper to layers of such 
sheets fifty feet or more in thickness. 

A study of the fossil remains of plants and animals should show us 
in what order these organisms lived and followed each other in times 
long past, and it is usually conceded that they do ; but, it is not an 
uncommon thing to find an earlier fossil layer lying above a later one. 
Geologists explain this by saying that changes have again taken place 
which reversed these lower beds, or thrust earlier strata between other 
layers. All this complicated arrangement lends itself to deceptive inter- 
pretation. For example, those who oppose the usually accepted geolog- 
ical evidence of "periods of time" and "successive ages" say that the 
arrangement of the various strata is so deceptive, that it can only be 
explained by a world upheaval of some kind, and that, therefore, no 
evidence of successive ages is worth anything. 1 

An interesting example of the order in which certain strata have 
been formed, is found in instances where trees and their stumps are 
found lying in a more or less semiupright position. Often the stump 
part and roots still lie in their position of growth, or at least they lie 
in a deeper stratum than the upper and less heavy portion. Such trees 
were either pushed over by a stream of water, or carried along by the 
stream. The heavier end became caught or weighted, and sank, while 
the upper end remained in a slant position in the direction of the current. 
It is, of course, also possible that the trees were entirely submerged 
while still growing. In the latter case, however, the rate of sand deposit 
must have been sufficiently rapid to lay down an accumulation of at least 
forty feet (enough to cover the erect tree) before the wood decayed. 

Former regions have been identified by the occurrence of great 
quantities of driftwood found in the strata, as having been quite close 
to land ; while differences in climate are evidenced by the finding of- 
tropic plant and animal remains in cold regions, and arctic plants and 
animals in tropic regions. 

Migrations of plants and animals from one region to another are 
demonstrated by the finding of fossil remains in different types of strata 
in different ages. 

1 G. McC. Price, "The Fundamentals of Geology." 

398 General Biology 

However, no one can tell the number of years required to lay down 
the various strata any more than he can tell how many years elapsed 
to form the intervals between such laying down; and these intervals 
no doubt were often much longer than the time it took to form the 

Intense cold or heat, resulting from a climatic change, undoubtedly 
killed many organisms which were unable to adapt themselves to the 
changing conditions of the past; while mountain ranges, becoming ele- 
vated, cut off the moisture-supply of others who went the same way. 

The glacial period is considered synonymous with the permian, and 
represents the extreme of cold, while the tropical period, the extreme of 
heat, is represented by coal beds (Fig. 245). 

The mechanics of adaptation of living organisms to new climatic 
and environmental changes has given rise to much speculation. 

Lamarck thought that the organism was directly affected by any 
change in environment and that this change then affected the germ- 
plasm so that the change in the parent could be inherited by the organ- 
ism's offspring, and thus result in a permanent racial change. 

Others taught that both somatoplasm and germplasm are simulta- 
neously affected. This theory is known as that of parallel induction. 

Darwin, like Lamarck, believed that small environmental changes 
became large ones as they were successively inherited. In fact, this was 
held by nearly all the early workers since the time of Darwin. But, as 
no evidence has been forthcoming which could explain how such en- 
vironmental changes could affect the germplasm and thus be inherited, 
biologists are inclined to hold with Professor H. H. Newman, that 
"external factors accelerate or retard processes that were already under 
way in the germplasm, so that the response appears to be something 
new in kind when it is only the result of a sudden acceleration of a 
character evolution already under way. Whatever be the underlying 
mechanism involved in adaptive changes, there is no hope of explaining 
adaptations on the Darwinian basis, through the selection of the best 
out of a vast area of purely fortuitous variations ; for if the historical 
study of vertebrate evolution reveals one thing more clearly than any 
other, it is that evolutionary changes are ordinarily progressive, and 
determinate in character, and that in many respects these ordinary 
processes of evolution are independent of each other and of environ- 
mental changes." 

This means that we need not hold that animals always adapt them- 
selves to their environment, but that they can migrate to environments 
which are best suited to them. And there is ample evidence to show 
that such migrations took place quite often. Some of these are shown 
by the land-bridges (over which animals passed) now destroyed, which 
connected islands and continents with each other. The animals were 
then shut off from their original home by the destruction of the bridges. 
Such animals are said to be geographically isolated. 



Not only have animals migrated, but as already stated, the climate 
itself migrated. This is shown by the fact that the marine and glacial 
coverings of the land's surface took place at much later periods in some 
places than in others. 

To return to the fossils themselves, it is necessary for the student 
to understand the various forms in which fossil remains come down to 
us. Bones may be buried in silt which then hardens. Later, water, con- 
taining minerals, may make its way through the silt and bit by bit dis- 
solve the bone, and deposit a mineral in its place. This is petrification. 
The shape and form of the bone remain intact, although the original 
bone-substance is replaced by a mineral. 

Fig. 246. 

Mammoth found frozen in Siberia. The skin is mounted 
in the museum of Petrograd in the posture in which it was 
found. (From Lull's "Organic Evolution," by permission of 
the Macmillan Co., Publishers.) 

Or, an organism may retain its form long enough to have the sur- 
rounding substance completely encase it and harden. As time goes by 
the organism is dissolved and disappears, while the hollow space it occu- 
pied remains. Such hollow forms, in the shape of organisms no longer 
present, are called molds. Investigators fill these molds with a material 
such as plaster of paris (which hardens easily) and obtain a cast of the 
original organism. 

Then, too, as stated above, the tremendous pressure of the upper 
layers may crush the fossil forms beneath, or the minerals which caused 
petrification may be re-dissolved, so as to expose the fossil remains to a 
condition which destroy* them, and this may happen after they have 
been so encased for thousands of years. Weathering and erosion may 
also expose fossils to the harmful effects of the weather. 

When very definite fossil remains are always found in certain strata, 


General Biology 

they are often called "index fossils," as such fossils can be used to deter- 
mine the place and period of the strata from which they are taken. 

One of the most interesting finds in 1901 was that of an ancient 
animal, whose species is now extinct, that of a mammoth found frozen 
in the ice of Siberia (Fig. 246), whose flesh was in excellent condition. 

In oil-bearing sands many excellent fossil specimens have also been 
well preserved. 

But the fossil remains, which have excited most discussion and spec- 
ulation, are those which are supposed to have belonged to human beings 
higher in the grade of life than the highest apes we now know, and yet 



Fig. 247. 

A. Remains of Pithecanthropus erectus ; the single femur shown in different 

B. Remains of the Neanderthal man in the Provincial Museum at Bonn. 

C. The Heidelberg Jaw. 

(A. From "The Open Court," B. from "Weltall V. Menschheit," C. from 
Bryce after Schoet Ensack.) 

distinctly lower than man. Authorities, however, disagree considerably 
as to what type of being these bones represented, some insisting their 
possessor was human, and some that he was not. 



One of the most important of these "finds" (1891-1892) is that of 
a part of a skull, two teeth, and a femur (Fig. 247, A). These parts lay 
at some distance from each other, so that we cannot be certain that they 
belonged to the same individual, but it is assumed they do. The shape 
of the femur indicates that its owner walked in an erect position and 
was about as tall as men now are. From the parts thus found a so-called 
"reconstruction" was made to show what the reconstructor thought the 
individual must have looked like. The name Pithecanthropus erectus is 
applied to the individual who once possessed these bones (Fig. 248). 
The bones are presumably from the early Pleistocene period. 

At another time a lower jaw with its teeth was found near Heidel- 
berg in Germany (Fig. 247, C). As the teeth are not ape-like, but ap- 
proach those of man, the individual who possessed them has been called 
Homo-heidelbergensis. The fossil remains of various animals found in 
the same region with the Heidelberg jaw give us the age of this find 
as that of the second interglacial period, which means that this jaw is 
only about one-half the age of Pithecanthropus erectus. 

In 1856 there was found in Prussia the skeleton of what is called 
the Neanderthal man (Fig. 247 B, and 248), or Homo-neanderthalensis 
which comes from about the fourth glacial period, so that it is about one- 
third the age of the Heidelberg man. 

Fig. 248. 

Restoration of prehistoric men. Left, Pithecanthropus 
erectus; middle, Homo neanderthqlensis, modeled on the 
Chapelle-aux-Saints skull; right, Cro-Magnon man, modeled 
on type skull of the race. (From the original husts of, and 
by courtesy of, Professor J. H. McGregor.) 

Then in France and Wales a number of skeletons have been discov- 
ered in which the skull is narrow and the face broad, something like that 
of the Esquimaux. The cheek bones and chin are also prominent. Pro- 
fessor J. H. McGregor has molded busts in accordance with his idea of 
what such men must have looked like (Fig. 248). 

There is no connection whatever between these various forms, so 
we cannot in any way prove that they are a genetically continuous 

402 General Biology 

series. All conclusions built upon these finds must, therefore, be purely 

From the evidence presented here, we note the fact that many pres- 
ent-day forms of both plants and animals are unlike their ancestors. 
We are, therefore, confronted with four possible explanations of why 
they are different: (1) that present-day forms are the lineal descendants 
of ancestral forms unlike themselves and that all new forms with ever 
increasing complexity spring from older ones ; (2) that new forms dif- 
ferent from the older ones have been created at different periods; (3) 
that all forms were brought into existence at about the same time, but 
due to a great world upheaval the fossiliferous strata have been so 
confusedly arranged that, while all fossils are of one age, it is our 
mistaken interpretation which makes us believe they are of different 
ages ; or (4) that organisms came into existence which, at the time of 
their origin, had the possibility of change placed within their germ- 
plasm, but which had to await the proper conditions of food and environ- 
ment before they could come forth to produce present-day forms. 

If it be accepted that any present-day forms are different from their 
ancestors, and that these new forms can produce offspring capable of 
transmitting that change to their posterity in turn, we must speak of an 
evolution as having taken place. 


Karl von Zittel's "History of Geology and Paleontology." 

A. Dendy, "Outlines of Evolutionary Biology." 

H. A. Nicholson, "Manual of Paleontology." 

Charles Schuchert, "Historical Geology." 

A. Morley Davies, "An Introduction to Paleontology." 

H. S. Williams, "Geological Biology." 

Articles on Geology, Paleontology, etc., in Encyclopedia Britannica. 



THE student must not forget when discussing evolution that this 
term means only that some present-day forms have become unlike 
their ancestors, and that such difference is then transmittable — 
in other words, that it has affected the germ-plasm. 

Evolution as it applies to the individual is, therefore, the name given 
a process by, and through, which an organism evolves or changes into 
a different type of being from its parents. 

In the chapter on genetics, we have seen how all offspring vary to 
a small extent, not only from their parents, but from each other. When 
such differences are slight, they are called variations and the organisms 
possessing them are known as varieties. When such variations become 
sufficient to set aside the new organism as a quite different type from 
its parents, the new types are known as different species. 

It will be noted that this is quite vague ; for, what one man may 
consider a difference sufficient to form a new species, another may not. 
There is, therefore, no good definition of the term species. Biologists 
disagree to a very marked extent as to what it means. 

Members of the. higher groups of animals are often considered as 
belonging to the same species if they can inter-breed and give birth to 
fertile offspring in turn. But, if we are to accept this definition, there 
never can be any strictly new species ; for, if animals can inter-breed, 
their offspring will belong to the species to which their parents belong, 
and if they cannot, there will be no offspring. 

Then, there are those who take the position that only those indi- 
viduals form true species which always breed true. If we accept this 
definition, it may be said that whenever a so-called new-form or mutation 
(as it is called) comes forth, such new form is in reality only the return 
of some ancestral type, which has been formed by the meeting of an egg 
and a sperm, both of which carried recessive characteristics. From this 
angle one may always explain new species as being old ones, again 
coming forth. 

However, species generally mean groups of individuals who possess 
similar outstanding characteristics, which characteristics can be trans- 
mitted to their offspring. 

First, then, in discussing evolution, one must be convinced that new 
species really do come into existence, otherwise there can be no evolu- 
tion. Practically all biologists now hold that new species do come into 
being, which means that they accept evolution as a fact. There is, how- 

404 General Biology 

ever, a vast difference of opinion as to the limitations within which 
evolution operates, both in the individual and in the race, as well as to 
the method by which evolutionary changes come to be what they are. 

Secondly, if all present-day forms have sprung from ancestors unlike 
themselves, the question arises as to whether all the different phyla 
sprang from one original living being (whether evolution is mono- 
phyletic or monogenetic), or whether there were numerous "first forms" 
from which all successive forms spring (polyphyletic or polygenetic 

Having settled for ourselves whether evolution is a fact, we set 
about trying to find a theory which will account for that fact. 

Only two great theories have been advanced. One by Charles 
Darwin, known as Darwinism, or Natural Selection, and the other by 
Korschinsky, and De Vries, known as the Saltation or Mutation theory, 
or heterogenesis. 

Darwinism holds that, as we have seen, the offspring of a single pair 
of flies will be almost six billion in ninety days if all eggs were to hatch. 
It follows that were such increase to continue in all animals and plants, 
the food-supply would soon become exhausted. There must, therefore, 
be a struggle for existence to determine which plants and animals are 
fittest to survive. 

Everyone has noted that millions of eggs, maggots, and insects 
never reach the adult form of life because they are eaten by various 
animals. The number of flies and other insects is, therefore, dependent 
upon the number and activity of their natural enemies as well as their 
own physical ability to avoid such enemies, together with their ability 
to obtain a sufficient supply of food and water for themselves. 

It follows that there will be a struggle even among the same group 
of organisms for food and water, while the whole group must struggle 
against their many natural enemies. Nature, through such struggle, 
selects the strongest and most active (as these are the only ones which 
will not succumb to the struggle) to carry on the race. The particular 
characteristics which make it possible for plants and animals to survive 
in this struggle for existence, are said to have a survival value. 

Darwin accepted variations in all living organisms as a fact, and 
built his theory on that fact. He contended that useful variations by 
possessing a survival value were transmitted to the offspring of such 
organisms, so that each succeeding generation received the advantage of 
its parents' acquired characteristics. 

However, it is generally held now that acquired characteristics are 
practically never inherited, and that natural selection only explains why 
certain organisms did not die and others did. It cannot explain the 
origin of new species. 

Darwinism is based on the assumption that very minute changes 
are constantly taking place in the organism. These changes have an 

Evolution 405 

effect on the germ-plasm of the individual, thus altering it and causing 
the change to be transmitted. For example, a giraffe by constantly 
eating food from trees, finds it necessary to reach higher and higher. 
This stretching of the neck will, then, in each generation cause the 
young giraffes to be born with a slightly longer neck. 

If such a change makes the individual better able to adapt itself to 
its surroundings and thus gives it an advantage in the struggle for exist- 
ence, it is said to be a selective factor. 

The mutation theory, contrary to the Darwinian, insists that sudden 
jumps, or great changes, take place, which are then transmitted. This 
theory is based on the fact that there are in nature so-called "freaks" 
or "sports" which suddenly spring forth. 

The crooked-legged sheep is the classic example. A New England 
ewe gave birth to a peculiar, crooked-legged ram. The shrewd Yankee 
farmer, who owned the sheep, saw in this crooked-legged ram an animal 
that could not jump fences, and so kept it. The crooked-leggedness 
proved to be a Mendelian dominant character which is transmitted from 
parent to offspring. There are now great numbers of the descendants 
of this single New England crooked-legged ram, which are in turn 

Such mutations can be explained by assuming that the recessive 
characters in egg and sperm have met after lying dormant for many 

In fact, there are a number of examples of characters lying dormant 
and being carried on from parent to offspring, only coming forth at 
certain times when the mating organism likewise has a similar dormant 
or recessive character. For instance, many mullein plants will, in certain 
years, suddenly produce longer leaves than is normal for that plant, thus 
showing that the cause of the longer leaves must be in the germ plasm 
of the varying plants. For, if such were not the case, there would not 
be so many to develop longer leaves in the same generation. 

In other words, this means that there is a peculiar arrangement of 
genes in the chromosomes of the mating-plants, and these genes have 
united to cause a similar abnormal development in all those plants which 
spring from similar zygotes. 

It is for reasons of this kind that biologists have come to the con- 
clusion that environment does not change the organism to any appre- 
ciable extent in its genetic value, but, that whenever changes come forth, 
these are due to changes in the germ plasm. 

To the two great theories mentioned above, there have been added 
at various times what might be called sub-theories or part-theories to 
account for certain developmental characteristics. The most prominent 
of these is known as Orthogenesis. Eimer and Nageli are its sponsors. 
Orthogenesis means that there is something in the organism which, once 
a line of development has begun, will enable the organism to continue 

406 General Biology 

in that certain line of development even though it kill the individual. 
An example, which comes to mind, is the teeth of rodents. These, 
when the animal becomes older and is unable to chew the hard sub- 
stances it did when young, continue to grow with the same undiminished 
vigor that they did when they were constantly being worn down by 
contact with hard substances, so that they may, as in the beaver, force 
the mouth open and starve the animal to death. 

But orthogenesis must be explained, and various reasons have been 
suggested to account for it, the reasons varying according to the "phi- 
losophy of life" of the one who is doing the explaining. 

Those who hold that all things are to be explained in terms of 
physics and chemistry, attempt to explain orthogenesis in physico- 
chemical terms. Those who hold that there is an inner driving force in 
all living matter which cannot be explained by physics and chemistry, 
insist that it is this inner driving force, or "vitalistic principle," which 
alone can account for it. 

Both sides, however, agree that the cause for this development is 
not in the organism's environment, but must be sought for in the organ- 
ism itself. As Professor Borradaile puts it, "the part of the environment 
is to decide which of the experiments of the organism are failures." And 
there is sufficient evidence to accept his statement. For instance, the 
fertilized egg-cells of nearly all the higher organisms are quite alike, yet 
they develop quite differently. And they retain this difference in devel- 
opment, even if the egg is transplanted into the body of a different kind 
of animal and is there allowed to develop to maturity. There must be 
a difference in the environment of the organs within the bodies of differ- 
ent animals, yet the egg grows on as it would have done under its normal 

When such definite direction takes place it is called purposiveness. 

The objection raised against the physico-mechanists (those who be- 
lieve that all things can be explained in terms of physics and chemistry) 
by those who do not hold to their point of view (vitalists), is that the 
body cannot be accepted as a machine in any true sense of the word. A 
machine produces a very definite and single type of work, while the 
living organism has all its work directed toward its own welfare, and 
unlike any machine known, can, when it is injured, direct its entire 
working system toward repairing itself in addition to continuing its 
regular work. It not only heals the wound inflicted, but actually grows 
new material, as we have seen by the regeneration experiments in 
Planaria and Arthropoda. 

Then, too, there is a decided chasm dividing living and non-living 
matter; so much so, that it is a common dictum of Biology that abso- 
lutely no life can come from non-living matter. There is no single 
case on record of any organism coming into existence except as the 
offspring from some other organism. 

Evolution 407 

However, as we know living things did not exist always, there must 
have been a time when they did come into existence. The physico- 
mechanists say, that while no living matter comes from non-living 
to-day, yet, as there must have been a time when it did, we must 
assume that different conditions once held sway from those we now 

But, such being the case, we break the most important law known 
to science — that of continuity. It is for this reason that it has been said, 
that the breaking of this law of continuity is the only heresy known to 
evolutionary science. 

The theory that life always comes from life is known as biogenesis, 
while the theory which holds that life can come from non-living matter 
is called abiogenesis. 

It will be noted that the evolutionary theories so far discussed have 
only taken the physical side of the individual into consideration to the 
entire neglect of the mental and intellectual. 

It was Alfred Russel Wallace, co-founder with Darwin of the nat- 
ural selection theory, who saw this quite early, and insisted that the 
psychical or mental side must also be considered if we are to form truly 
valid conclusions. He contended that once mentality enters, as it does 
in man, such an organism could use this mentality to set aside or change 
the physical selection which nature carried on. In other words, the 
earlier evolutionists were interested in the structure of nerves and nerve 
elements, while Wallace saw the necessity of taking the thought which 
is carried by the higher nerve centers into consideration. 

It is well for the student to know both the evidence adduced in 
support of evolution and evolutionary theories, and the objections which 
have been hurled against it. We have, therefore, summed up the argu- 
ments of both sides, whether such support and objections are always 
conclusive or not. 


1. Paleontological. 

(a) Many new kinds of plants and animals are found in each suc- 
cessive strata as shown by their fossil remains. 

(b) The later organisms are more complex than earlier ones. 

(c) The more recent fossils prove that they are quite closely' 
related to the modern forms now living. 

2. Genetics. 

Breeding experiments, as well as observation, prove that all organ- 
isms are constantly varying, and that constant variations in the same 
group of organisms are transmitted to succeeding generations. 

408 General Biology 

3. Comparative Anatomy. 

The similarity of structure in different individuals is precisely what 
would be experienced if evolution did take place. 

Homology (similarity of structural development) is to be regarded 
as a sign of relationship- as it is assumed that in such cases little or no 
structural change has taken place in times past. Contrariwise, organ- 
isms which are quite dissimilar in structure are assumed to have 
diverged many years ago. 

4. Comparative Embryology. 

(a) Likenesses between embryos of different animals are assumed 
to demonstrate a close fundamental relationship and a common ancestor. 
An example often quoted is that of Sacculina (Fig. 212), a parasite on 
the abdomen of the crayfish. This parasite is merely a rounded, pulpy 
mass with no clearly defined structure except a little root-like projection, 
which extends into the body of the host to absorb the fluids. The em- 
bryo of Sacculina, however, is a very definitely shaped three-cornered 
little organism with jointed legs and all other necessary features which 
bring it under the crustacean classification. In fact, it is practically a 
degenerated barnacle. 

(b) All higher forms of vertebrates possess so-called gill-pouches 
during the embryonic stage, although the higher forms do not retain 
them in the adult stage. This would lead to the assumption that the 
common ancestors of vertebrates must have been fish-like. 

(c) According to von Baer and Haeckel, all animals during the 
embryonic period pass through the adult forms of the race to which 
they belong, thus presenting conclusive evidence of the history of their 

5. Comparative Physiology. 

(a) Animals, which are closely related genetically, have a some- 
what similar blood-composition, as proved by the fact that the blood 
of one such related animal can be successfully transfused to another 
without harm. 

(b) The test described in Chapter XIV by which human blood 
can be differentiated from that of many lower mammals, does not differ- 
entiate human blood from the blood of the higher apes. 

6. Geographical Distribution. 

Animals such as marsupials (pouched animals), which have as much 
in common structurally as the Australian kangaroo and the American 
opossum, while yet quite unlike in general appearance, can only be 
accounted for by taking into consideration the geological evidence for 

Evolution 409 

a land-bridge which once connected Australia and America. The two 
animals having had the same ancestry, changed their appearance because 
of a changed geographical environment, although their general structure 
has remained quite as it was. 

There are no native ungulates in Australia, although there is no 
reason why there should not be if other than evolutionary methods have 
been factors in producing new types of animals. 

Or, again, one finds, for example, on the west coast of South 
America, peculiar animals found nowhere else in the world, while on the 
neighboring islands there are animals resembling those on the coast 
of the continent both in structure and habit, yet sufficiently different 
to be called new species. 

7. Natural Selection. 

This is an attempted explanation of why present-day forms are what 
they are, by showing that food is never equal to the possible rate of 
increase in living forms. Such lack of food causes a struggle for exist- 
ence, through which struggle the weakest (the ones being least adaptive) 
go down, while the stronger (those best able to adapt themselves to 
their environment) survive. 

Natural selection describes the causes which have prevented sur- 
viving forms from becoming extinct. 


The arguments which are usually brought forth to oppose these 
evidences for evolution are as follows : 

1. Paleontology. 

(a) The different kinds of plants and animals found in various 
geological strata can only demonstrate that similar organisms were 
either larger or smaller than others, or varied in ways which can be 
accounted for by a difference in the temperature and food supply of 
different ages. Examples of this are the horse and mammoth. Then, 
too, paleontologists insist that their finds can only be explained by 
assuming that acquired characteristics are inherited, although experi- 
mental evidence seems to point against this being true. 

(b) The so-called increasing complexity on the part of so-called 
"younger" fossils as compared with so-called "older" ones, may always 
be explained by assuming that Mendelian recessive characteristics have 
again come forth, and that consequently the so-called "new forms" are 
really a return of old ones. 

(c) Recent fossils are like modern forms because the climatic 
changes and the food supply have not varied much during the interval 

410 General Biology 

between our own time and the time when the prototypes of these recent 
fossils lived, and examples of so-called older forms (those which lie 
above the recent forms) can be considered evidence for this statement, 
(d) Those who insist on experimental evidence which is always 
under the control of the experimenter, say that fossil-remains furnish us 
only with "descriptions" of what is found. It is a "dead" account. It 
can never give us an explanation. Explanation and interpretation can 
only come through our logic. Paleontological evidence is, therefore, all 
logical and not experimental. A strictly scientific explanation from the 
experimentalist's point of view must also present experimental evidence. 
This has not been, and cannot be, done in paleontology. 

2. Genetics. 

Inherited changes can always be referred back to ancient Mendelian 
recessives meeting, and thus producing a "past" type. No strictly "new" 
types can ever be formed because the chromosomes never die (so long 
as there are living offspring), and all that ever happens is that some 
part of them is thrown out. But, from Avhat is known of Biology, it is 
impossible to add anything to the offspring which is not already present 
in the chromosome content of the germ cells. 

3. Comparative Anatomy. 

Similarity of structure by no means proves relationship, as shown 
by examples of convergent evolution, where tv/o quite dissimilar struc- 
tures come to look alike in various aspects, due to similar functioning. 
Witness such experiments as Carey's in which bladder-muscle was con- 
verted into beating heart-muscle by causing the bladder to simulate 

The argument from comparative anatomy holds good only if one 
accept the dictum that "structure determines function," while the experi- 
ment just mentioned shows that function determines structure, once one 
has the material with which to work. 

4. Comparative Embryology. 

(a) Any organ not used is likely to degenerate. This accounts for 
Sacculina degenerating when it assumed a parasitic habit where it no 
longer uses the various organs it once used. This is not remarkable, 
and if it proves anything, it proves only that an organism can lose 
something it once possessed, though it by no means proves that what 
we have been considering a more complex organism, can arise from one 
that is less complex. 

(b) The so-called gill-pouches demonstrate only as in (c) that 
vertebrate forms pass through similar stages of growth and not that 
one springs from the other. 

Evolution 411 

(c) If the Haeckelian law is to hold good, that embryos pass 
through the adult stages of the race to which they belong, we are con- 
fronted with some unacceptable conclusions. For instance, only the 
human being walks in an entirely upright position. In man alone there 
are in the developing brain three complete bends which remain through- 
out adult life. It is assumed that only his upright position can account 
for the third bend, which brings the cerebral hemispheres back over the 
brain-stem. But in the chick, and in practically, if not all, vertebrates, 
these three bends take place in the embryo. It is later that at least one, 
and sometimes two, of the bends disappear. We must, therefore, assume 
that frogs, chicks, lizards, etc., once walked erect like man, an assump- 
tion that not even the most ardent defenders of the Haeckelian law 
will admit. 

5. Comparative Physiology. 

(a) Similarity of blood-composition in quite similar forms is to be 
explained again on the principle that all similar forms go through a 
similar development, and that with similar food and temperature, the 
blood must necessarily be quite similar because it must draw its com- 
ponent substance from the same food material. 

(b) Since the blood of a hybrid-form, such as the mule, reacts 
differently from that of either of its parents, we do not know, until 
further research brings forth more proof, that similarity of reaction in 
blood-tests is a valid test of relationship. 

6. Geographical Distribution. 

This, like natural selection, can only show why some organisms 
survived. It throws no light on origins. It can show how parts of an 
organism may be lost, but not how additional complexity has come. 

7. Natural Selection. 

This explains nothing of importance. It fails utterly to explain the 
degeneration of useless organs, and why variations of great magnitude 
do not occur more often, as well as why and how a simultaneous varia- 
tion in different parts of the body takes place to improve a definite 

8. Psychology. 

All the evidence evolutionists adduce to prove their arguments is 
invalid because they take only the physical side of the organism into 
consideration, forgetting* the most important part — the mental. 

412 General Biology 

9. Logic. 

We have been reversing the order of things, by forgetting that, if 
a tiny cell or organism has the ability or potentiality of becoming a 
highly complex animal, it must be much more complex than the later 
organism into which it is to grow. For, surely the smaller an object 
may be, which can contain all that it is later to become, the greater in 
complexity it must be. And, if such a tiny object is so intensely com- 
plex, it could not have suddenly sprung into existence without an intelli- 
gence of some kind arranging it. 

10. Physics. 

The student of depth has been driven into out-and-out skepticism 
of anything being true in science, or has gone over entirely to mysticism, 
because he cannot overcome the obstacle which the acceptance of the 
laws of the different laboratory sciences place in the way of his bio- 
logical findings. For example, physics tells him that no more work 
can be obtained from a machine than is put into it, and that nothing 
can rise higher than its source. Then the evolutionist tells him (in 
contradiction to these laws) that more complex forms come from those 
less complex. This belies both laws, for intelligence is certainly some- 
thing higher, and more than non-living matter. And intelligence cannot 
be explained in terms of either physics or chemistry. 

If it be told the student that the energy of the sun furnishes the 
energy which can do all these things, and that there is a law known as 
the conservation of energy, he will read the statement of various eminent 
physicists who tell him that the sun's heat will gradually become 
less and less, finally becoming entirely dispersed. Consequently there 
will not be as much as there once was, and the law is broken. This 
brings him back to the place from which he started. "How did the 
energy and the potentiality of a simple organism become complex, and 
how did the developing intelligence become what it is, unless it got it 
from something still greater?" 

11. Language and Intelligence. 

If it be proved that plants and animals have arisen in an ever- 
ascending plane, how account for articulate language and intelligence 
(true ability at thinking which is then expressed in words) ? Can this 
psuchus or psychon, or real intellectual part of man, have come from 
anything less than a still greater intelligence? 

12. Continuity. 

As was shown in the chapter on the history of Biology, the very 
foundation of science, as now understood, is based on the law of con- 

Evolution 413 

tinuity, namely, that the laws of nature never vary. Yet we find all 
biologists agreeing that the law of continuity has been broken, by the 
fact that living forms must have once sprung from non-living, a con- 
dition now no longer true. This is the great "heresy" of evolutionary 
science. As life and mentality do not now operate as they once did, 
when, where, and how did they begin? 

13. No Satisfactory Theory of Evolution. 

No theory of evolution yet propounded is satisfactory because none 
has satisfied the requirements set forth above. 

14. Impossibility of a Satisfactory Physical Explanation. 

There exist certain rays, known as infra-red and ultra-violet, which 
no human eye can see ; yet, these rays can be proved to exist by the 
physicist. If the ultra-violet rays are thrown upon a group of brown 
ants they will immediately scatter quite hurriedly, thus demonstrating 
their ability to sense rays which man cannot. 

Now, it is probably from such evidence as this that one biologist, at 
least, draws the conclusion that just as there are undoubtedly thousands 
of colors which no human eye can see, and thousands of sounds no 
human ear can hear, so there must be thousands of factors in every 
explanation which the human mind cannot grasp. This being true, it 
follows that, if we can find any explanation which is plausible, and which 
fits in with every nook and crevice of our mind, we know that such a 
theory is not likely to be true, because there are thousands of points 
that we must necessarily have neglected to consider due to our sheer 
intellectual inability. Thus even the most plausible arguments are 


We have presented practically all of the important arguments for 
and against evolution itself and the various theories which attempt to 
account for it, because it is just as essential for a well-educated man to 
know the opposing arguments in any given case as it is for him to know 
the supporting ones. The theories which the student is to accept are 
those which he finds sufficient evidence for in his work throughout his 
laboratory course. 

Regardless of what one may believe that the evidence has brought 
forth, all biological workers must accept evolution as a scientific- 
hypothesis, though this does not mean that they must accept any of the 
theories propounded to account for it. The above statement is true, 
because there is much more evidence to show that an evolution has 
taken place than there is to show how and why it took place. 

Then, too, the student must note the difference between the cause 

414 General Biology 

of evolution (which the various evolutionary theories try to explain) 
and the course of evolution. This latter is only a description of what 
has been found, as, for instance, the charts which show the various 
fossil-remains of what are considered the ancestors of the horse and 
mammoth. Such charts, of course, explain nothing. 

The Darwinians originally held to the doctrine that all variations 
must possess some function of a survival value, but we now know that 
characters which are a decided hindrance in the survival sense, are 
inherited and passed on from one generation to another just as readily 
as those which are of value. 

Two different types of organisms may often grow to be quite alike, 
or at least certain organs may develop so as to appear alike if they 
function alike. This growing alike is known as convergent evolution. 
Individuals originally structurally alike, which later become dissimilar, 
are said to do so through divergent evolution. 

From what has been said above, one is likely to agree with the 
writer who said that every biologist seems to have his own pet theory 
to account for the evolutionary process. 

Notwithstanding this fact, one must, however, have some kind of 
a gauge by which to measure the plausibility of a proposed theory. 
Otherwise there is not even an approach toward finding whether any 
given evidence is of value. 

It is to assist the student in forming such a gauge that the following 
seven questions are here tabulated. These must be answered by any 
theory which is to win complete and final acceptance. 


These questions refer to organic evolution in its widest signification, 
as referring to both the individual and the race. 

(1) How did life originate? 

(2) How can a more complex individual develop from ancestors 
which were less complex? 

(3) How can an organism adapt itself to its surroundings? 

(4) What causes the so-called mechanically directed type of 
variations known as orthogenesis? 

(5) What causes the series of the many undoubtedly purposive 

(6) What causes the factors of heredity to behave as they do? 

(7) What factors can account for mentality and intelligence 
(which are non-physical things) arising from physical and non-mental 

Evolution 415 


Charles Darwin, "The Origin of Species by Natural Selection." 

Delage and Goldsmith, "The Theories of Evolution." 

Vernon L. Kellogg, "Darwinism To-day." 

Lull, Barrell, Schuchert, Woodruff, and Huntington, "The Evolu- 
tion of the Earth and Its Inhabitants." 

Henry M. Bernard, "Some Neglected Factors in Evolution." 

Lawrence J. Henderson, "The Order of Nature." 

S. Herbert, "The First Principles of Evolution." 

Thomas Hunt Morgan, "A Critique of the Theory of Evolution." 

Erich Wasmann, "Modern Biology and the Theory of Evolution." 

Erich Wasmann, "The Problem of Evolution." 

N. C. Macnamara, "The Evolution and Function of Living Pur- 
posive Matter." 

A. D. Darbishire, "An Introduction to a Biology." 

George McCready Price, "The Fundamentals of Geology." 

George McCready Price, "The Q. E. D." 

James Johnstone, "The Philosophy of Biology." 

S. J. Holmes, "Life and Evolution." 

Edmund Noble, "Purposive Evolution." 

George H. Parker, "What Evolution Is." 



IT has already been shown that one may classify living things as to 
structure or function, that is, as to anatomy or physiology. The early 
naturalists felt that the most important thing in the study of living 
matter consisted in finding names and assigning definite places for 
every distinct individual. A little later morphology, or anatomy, was 
considered most important. Still later physiology, or the way an animal 
performs vital activities, was the all-important thing. Then with the dis- 
covery that urea, an organic compound, could be manufactured in the 

laboratory, much stress was laid upon chem- 
istry. Formerly it was quite common for 
naturalists to look for differences, in order to 
classify an individual, while now we look 
primarily for similarities in order to under- 
stand the close relationships which bind 
individuals into a common group. 

Classification is now no longer the prime 
factor in the study of Biology, and men, who 
are interested only in assigning names and 
groupings, are not considered scientists. It 
must not be forgotten, however, that there 
could be no science possible, and biologists 
would be unable to discuss their work intelli- 
gently with each other unless some method 
could be found by which each would know 
what the other was talking about. 
It is, therefore, well to know several of the important naturalists 
whose names are most intimately associated with this particular phase 
of Biology. 

John Ray (1627-1705), an Englishman, was the first real systematist. 
Following him came Carolus Linnaeus (Carl von Linne, 1707-1778), 
who is in reality the founder of our present method of classifying. In 
fact, one of the distinguished honors that may come to a botanist is to 
be elected a Fellow of the Linnean Society. Linne's important work 
was his Systema Naturae, consisting of twelve volumes, which appeared 
between the years 1735 and 1768. There was a thirteenth volume, added 
after his death. Linnaeus practically completed Ray's classification. He 
used structure as the basis of classification. There were six classes, four 

Fig. 249. 

Carl von Linne, 1707-1778. 
From G. Stuart Gager's 
"Fundamentals of Botany" by- 
permission of P. Blakiston's 
Son & Co., Publishers. 

Classification 417 

of which were vertebrate and two invertebrate. These classes were in 
turn divided into orders, the orders into genera, and the genera into 
species. However, the Linnaean Genus sometimes includes three or 
four orders of our present arrangement of groups. 

Following Linnaeus came Georges Cuvier (1769-1832), who in turn 
was followed by De Blainville (1777-1850). The latter's method is 
considered superior to that of Cuvier. 

Lamarck (1744-1829) classified animals according to their nervous 
sensibilities, speaking of apathetic animals, that is, those without nervous 
systems, or apparent sensations, among the invertebrates, and the 
sensitive animals, largely also among the invertebrates, while the intelli- 
gent animals corresponded to the vertebrates. 

Then came Oken (1779-1851), who suggested two different methods 
of classifying. Neither one, however, received much recognition. One 
of his systems was based upon the arrangement of organs, while the 
other was based upon the senses. The latter were divided into such 
interesting but valueless groups as Dermatozoa (literally, skin or touch 
animals), by which he meant the invertebrates; the Glossozoa (literally, 
tongue animals), the fishes; the Rhinozoa (nose animals), which 
included the reptiles; the Otozoa (ear animals) or the birds; and another 
class, which appears to have been called interchangeably the Ophthal- 
mozoa (eye animals) or Trichozoa (hair animals), the mammals. It 
would be hard to name a set of distinctions less applicable as classifica- 
tion marks than most of these. 

Pierre-Latreille (1762-1833), Johannes Muller (1801-1858), and 
Louis Agassiz (1807-1873), should also be mentioned among the sys- 

The Linnaean system has been adopted because it introduced a 
sharply defined grouping and a definite terminology. In other words, 
this system permits a grouping of forms which resemble each other, as 
well as a grouping according to relationships other than physical 

As already stated, Linnaeus used four general groupings : class, 
order, genus (plural, genera), and species. Modern systematists have 
added phylum (plural, phyla), subphylum (assemblies greater than the 
class), class, subclass, order, suborder, family, subfamily, genus, sub- 
genus, species, subspecies, and sometimes others. 

The following table will illustrate the present method of naming and. 
classifying animals: 

Phylum. Protozoa. 
Class. Rhizopoda. 
Order. Lobosa. 

Family. Amoebidae. 
Genus. Amoeba. 

Species. Proteus. 

418 General Biology 

The botanists use a somewhat different classification, but the one 
here given is the one of greatest value and importance to the student. 
All zoologists, although accepting this classification, do not necessarily 
classify the same animals under the same heading. This often leads to 
considerable confusion for the beginner. 

The student of medicine will find that during the past twenty years 
a definite nomenclature has been adopted in the study of human anatomy 
known as the B. N. A., so called because it was brought about at an 
International Anatomical Conference at Basle, Switzerland, and there- 
fore called the Basle Nomenclatura Anatomica. 

The Linnaean system designates the species by two Latin or Latin- 
ized names: the generic name, a noun; and the specific name, usually an 
adjective. To this is added a third, if a subspecies is recognized. A sub- 
species is usually more or less synonymous with variety in classification, 
although variety is sometimes used ; in fact, in one group, ants (family 
Formicidae), there are usually four words in the name. 

The rules applying to the nomenclature, although following Linaeus 
are set forth in various codes. These are the British Association Code, 
the American Ornithological Union Code, the Code of the German 
Zoological Society, and the Code of the International Zoological Con- 
gress. The International Code of Zoological Nomenclature, adopted by 
the International Zoological Congress and governed through a Commis- 
sion on Nomenclature is used almost everywhere now. Professor Schull 
has summed up the principal rules as follows: 

"The first name proposed for a genus or species prevails on the con- 
dition that it was published and accompanied by an adequate description, 
definition or indication, and that the author has applied the principles 
of binomial nomenclature. This is the so-called law of priority. The 
tenth edition of the Systema Naturae of Linnaeus is the basis of the 
nomenclature. The author of a genus or species is the person who first 
publishes the name in connection with a definition, indication, or de- 
scription, and his name in full or abbreviated is given with the name; 
thus, Bascanion anthonyi Stejneger. In citations the generic name of 
an animal is written with a capital letter, the specific and subspecific 
name without initial capital letter. The name of the author follows the 
specific name (or subspecific name if there is one) without intervening 
punctuation. If a species is transferred to a genus other than the one 
under which it was first described, or if the name of a genus is changed, 
the author's name is included in parentheses. For example, Bascanion 
anthonyi Stejneger should now be written Coluber anthonyi (Stejneger), 
the generic name of this snake having been changed. One species con- 
stitutes the type of the genus ; that is, it is formally designated as typical 
of the genus. One genus constitutes the type of the subfamily (when a 
subfamily exists), and one genus forms the type of the family. The type 
is indicated by the describer, or if not indicated by him, is fixed by 

Classification 419 

another author. The name of a subfamily is formed by adding the 
ending inae, and the name of a family by adding idae to the root of the 
name of the type genus. For example, Colubrinae and Colubridae are 
the subfamily and family of snakes of which Coluber is the type genus." 

Since evolution has become more or less a keynote in the study of 
Biology, it has been the desire of biologists to group living structures 
according to a common ancestry. This idea has been in the minds of 
systematists since Darwin's time. 

Similarity of species of a given genus is supposed to indicate kin- 
ship, so that the individuals among any given genus show greater 
diversity than do the members of the species going to make up that 
genus, although all members of the genus have something in common. 
We may take as an example the vertebrates, which constitute the so- 
called highest phylum, and the protozoa — the single-celled animals— 
which constitute the so-called lowest phylum. Frogs being vertebrates, 
that is, having a backbone, are classified in the same phylum as man, 
who also has a backbone, but there is much greater difference between 
a frog and a man than there is between the many different species of 

As already stated, systematists have usually used structure for their 
important clue to affinities. "However," again quoting Professor Schull, 
"the evidential value of similarity in one or several structures unaccom- 
panied by the similarity of all parts is to be distrusted, since animals 
widely separated and dissimilar in most characters may have certain 
other features in common. Thus, the coots ( ), 

phalaropes ( ), and grebes ( ), 

among birds have lobate feet, but, as indicated by other features, they 
are not closely related; and there are certain lizards (Amphisbaenidae), 
( ), which closely resemble certain snakes 

(Typhlopidae), ( ), in being blind, limbless, 

and having a short tail. The early systematists were very liable to 
bring together in their classification analogous forms, that is, those 
which are functionally similar; or animals which are only superficially 
similar. In contrast with the early practice, the aim of taxonomists at 
the present time is to group forms according to homology, which is 
considered an indication of actual relationship. Since a genetic classifi- 
cation must take into consideration the entire animal, the search for 
affinities becomes an attempt to evaluate the results of all morphological 
knowledge, and it is also becoming evident that other things besides 
structure may throw light upon relationships. The fossil records, geo- 
graphical distribution, ecology, and experimental breeding may all assist 
in establishing affinities." 

It is, of course, necessary that, before any final classification can be 
made, one must know the various forms that exist and have existed in 
the past, and one of the greatest obstacles in this field is that most 

420 General Biology 

animals having a soft body have decayed and left no record of themselves 
among the fossil remains thus far found. Only those which possessed 
an intensely hard substance, or lived and died in regions where, due to 
the peculiar character of the soil or water, they were preserved, can 
furnish us with any accurate record of the past. 

There are men who have taken up individual studies in order to 
ascertain all the details of their given specialties, and such men are 
named after the study-group they have adopted as such specialty; for 
example, one who specializes in the study of protozoa is called a Proto- 
zoologist; one who studies worms is known as a Helminthologist ; one 
who studies mollusks, a Conchologist ; one who studies insects, an 
Entomologist, while he who studies birds is an Ornithologist, and he 
who studies mammals, a Mammalogist. 

It is, of course, understood that these men may not be interested in 
classification alone, but that they may be anatomists, physiologists, 
ecologists, etc., also in regard to their favorite study. 

The checking up of the different conclusions which different workers 
in the same field, and different workers in different fields, have arrived 
at, is one of the most interesting and valuable studies possible. This is 
particularly true, because so frequently all the evidence that a Paleon- 
tologist accepts, points to a totally different conclusion from that which 
the student .of experimental genetics finds to be true. The history of 
science is replete with cases of groups of men having held and defended 
doctrines most valiantly, and with seeming correctness, entirley opposite 
to those of men in other fields of study. 


Schull, "Principles of Animal Biology." 

H. C. Oberholser, "The Nomenclature of Families and Subfamilies 
in Zo61ogy." "Science," August 13, 1920. 



(After Hegner, Schull, Handlirsch, Brues, Melander, Muttkowski, 

and Wheeler.) 

Class I. Rhizopoda ( ) 

Order 1. Lobosa ( ) 

Order 2. Heliozoa ( ) 

Order 3. Radiolaria ( ) 

Order 4. Foraminifera ( ) 


Class II. Mastigophora ( 

Order 1. 

Flagellata ( 

Order 2. 


Order 3. 


Order 4. 

Cystoflagellata ( 

Class III. Sporozoa ( 

Subclass I. 

Telosporidia ( 

Order 1. 

Gregarinida ( 

Order 2. 

Coccidiidea ( 

Order 3. 

Haemosporidia ( 

Subclass II. 

Neosporidia ( 

Order 1. 

Myxosporidia ( 

Order 2. 

Sarcosporidia ( 

Class IV. Infusoria ( 

Subclass I. 

Ciliata ( 

Order 1. 

Holotricha ( 

Order 2. 

Heterotricha ( 

Order 3. 

Hypotricha ( 

Order 4. 

Peritricha ( 

Subclass II. 

Suctoria ( 



Class I. Calcarea ( 

Order 1. Homocoela ( 
Order 2. Heterocoela ( 

Class II. Hexactinellida ( 

Class III. Demospongiae ( 

Order 1. Tetraxonida ( 

Order 2. 

Monaxonida ( 

Order 3. 

Keratosa ( 


Class I. Hydrozoa ( 

Order 1. 

Anthomedusae ( 

Order 2. 

Leptomedusae ( 

Order 3. 

Trachymedusae ( 

Order 4. 

Narcomedusae ( 

Order 5. 

Hydrocorallinae ( 

Order 6. 

Siphonophora ( 


422 General Biology 

Class II. Scyphozoa ( 

Order 1. Stauromeclusae ( 

Order 2. Peromedusae ( 

Order 3. Cubomedusae ( 

Order 4. Discomedusae ( 

Class III. Anthozoa ( 

Subclass I. Alcyonaria ( 

Order 1. Stolonifera ( 

Order 2. Alcyonacea ( 

Order 3. Gorgonacea ( 

Order 4. Pennatulacea ( 

Subclass II. Zoantharia ( 

Order 1. Edwardsiidea ( 

Order 2. Actiniaria ( 

Order 3. Madreporaria ( 

Order 4. Zoanthidea ( 

Order 5. Antipathidea ( 

Order 6. Cerianthidea ( 

Class I. Turbellaria ( 

Order 1. Rhabdocoelida ( 
Order 2. Tricladida ( 
Order 3. Polycladida ( 

Class II. Trematoda ( 

Order 1. Monogenea ( 
Order 2. Digenea ( 

Class III. Cestoda ( 



Class I. Asteroidea ( 

Class II. Ophiuroidea ( 

Class III. Echinoidea ( 

Class IV. Holothuroidea ( 

Class V. Crinoidea ( 



Class I. 
Class II. 





Class III. 

Class IV. 


Archiannelida ( 
Chaetopoda ( 
I. Polychaeta ( 

1. Phanerocephala ( 

2. Cryptocephala ( 

II. Oligochaeta ( 

1. Microdrili ( 

2. Macrodrili ( 

Hirudinea ( 
Onycophora ( 

Class I. Amphineura ( 

Order 1. Polyplacophora ( 
Order 2. Aplacophora ( 

Class II. Gastropoda ( 

Subclass I. Streptoneura ( 

Order 1. Aspidobranchia ( 
Order 2. Pectinibranchia ( 

Subclass II. Euthyneura ( 

Order 1. Opisthobranchia ( 
Order 2. Pulmonata ( 

Class III. Scaphopoda ( 
Class IV. Pelecypoda ( 

Order 1. Protobranchia ( 

Order 2. Filibranchia ( 

Order 3. Eulamellibranchia ( 

Order 4. Septibranchia ( 

Class V. Cephalopoda ( 

Order 1. Tetrabranchia ( 
Order 2. Dibranchia ( 


General Biology 


Class I. Crustacea ( 

Subclass 1. Branchiopoda ( 

Subclass 2. 
Subclass 3. 
Subclass 4. 
Subclass 5. 
Subclass 6. 

Ostracoda ( 
Copepoda ( 
Cirripedia ( 
Leptostraca ( 
Malacostraca ( 

Class II. Merostomata ( 

Order 1. Gigantostraca ( 

Class III. Poecilopoda ( 

Order 1. 

Xiphosura ( 

Class IV. Linguatulida ( 

Order 1. 

Pentastomoidea ( 

Class V. Pantopoda ( 

Order 1. 
Order 2. 
Order 3. 

Clossendromorpha ( 
Nymphomorpha ( 
Pycnogomorpha ( 

Class VI. Arachnoidea ( 

Subclass 1. 

Cteiphora ( 

Order 1. 

Scorpiones ( 

Subclass 2. 

Lipoctena ( 

Order 1. 
Order 2. 
Order 3. 
Order 4. 
Order 5. 
Order 6. 
Order 7. 

Pedipalpi ( 
Araneae ( 
Meridogastres ( 
Opiliones ( 
Acarina ( 
Cheloneti ( 
Solifugae ( 

Class VII. Myriapoda ( 

Subclass 1. 

Opisthogoneata ( 

Order 1. 

Chilopoda ( 

Subclass 2. 

Progoneata ( 

Order 1. 
Order 2. 
Order 3. 

Symphyla ( 
Pauropoda ( 
Diplopoda ( 



Class VIII. Mirientomata ( 
Order 1. Protura ( 

Class IX. Collembola ( 

Order 1. Arthropleona ( 
Order 2. Symphopleona ( 

Class X. Campodeoidea ( 

Order 1. 
Order 2. 

Rhabdura ( 
Dicellura ( 

Class XI. Thysanura ( 

Order 1. 
Order 2. 

Lepismatoidea ( 
Machiloidea ( 

Class XII. Pterygogenea 

(Insecta sensu strictd), ( 

Subclass 1. 

Orthopteroidea ( 

Order 1. 
Order 2. 
Order 3. 
Order 4. 
Order 5. 
Order 6. 

Grylloblattoidea ( 
Orthoptera ( 
Phasmoidea ( 
Diploglossata ( 
Dermaptera ( 
Thysanoptera ( 

Subclass 2. 

Blattaeformia ( 

Order 7. 
Order 8. 
Order 9. 
Order 10. 
Order 11. 
Order 12. 
Order 13. 

Mantoidea ( 
Blattoidea ( 
Zoraptera ( 
Isoptera ( 
Corrodentia ( 
Mallophaga ( 
Siphunculata ( 

Subclass 3. 

Hymenoptera ( 

Order 14. 

Hymenoptera ( 

Subclass 4. 

Coleopteroidea ( 

Order 15. 
Order 16. 

Coleoptera ( 
Strepsiptera ( 

Subclass 5. 

Embidaria ( 

Order 17. 

Embiidina ( 


General Biology 

Subclass 6. 
Order 18. 

Subclass 7. 
Order 19. 

Subclass 8. 
Order 20. 

Subclass 9. 

Order 21. 
Order 22. 
Order 23. 

Subclass 10. 

Order 24. 
Order 25. 
Order 26. 
Order 27. 
Order 28. 

Subclass 11. 

Order 29. 
Order 30. 

Libelluloidea ( 
Odonata ( 

Ephemeroidea ( 
Plectoptera ( 

Perloidea ( 
Plecoptera ( 

Neuropteroidea ( 

Megaloptera ( 
Raphidoidea ( 
Neuroptera ( 

Panorpoidea ( 

Panorpatae ( 
Trichoptera ( 
Lepidoptera ( 
Diptera ( 
Suctoria ( 

Rhynchota ( 

Homoptera ( 
Hemiptera ( 


Group 1. 

Group 2. 

Group 3. 

Group 4. 

Group 5. 

Group 6. 

Group 7. 

Group 8. 

Group 9. 

Group 10. 

Mesozoa ( 
Nemertinea ( 
Nematomorpha ( 
Acanthocephala ( 
Chaetognatha ( 
Rotifera ( 
Bryozoa ( 
Phoronidea ( 
Brachiopoda ( 
Gephyrea ( 


Subphylum I. Cephalochorda or 
Adelochorda ( 



Subphylum II. Urochordata or Tunicata ( 

Order 1. Larvacea ( 
Order 2. Ascidiacea ( 
Order 3. Thaliacea ( 

Subphylum III. Hemichordata ( 

Order 1. Enteropneusta ( 
Order 2. Pterobranchiata ( 
Order 3. Phoronidia ( 

Subphylum IV. Vertebrata or Craniata ( 

Class I. Cyclostomata ( 

Subclass 1. Myxinoidea ( 
Subclass 2. Petromyzontia ( 

Class II. Pisces or Gnathostomata ( 

Subclass 1. Elasmobranchii ( 

Order 1. Plagiostomi ( 

Suborder I. Selachii ( 
Suborder II. Batoidei ( 

Order 2. Holocephali ( 

Subclass II. 

Order 1. 
Order 2. 
Order 3. 
Order 4. 

Teleostomi ( 

Crossopterygii ( 
Chondrostei ( 
Holostei ( 
Teleostei ( 

Subclass III. Dipneusti (Dipnoi), ( 

Class III. Amphibia ( 

Subclass I. Stegocephali ( 

Subclass II. Lissamphibia ( 

Order 1. Apoda (Gymnophiona), ( 
Order 2. Urodela ( 
Order 3. Anura ( 

Class IV. Reptilia ( 

Order 1. Chelonia ( 

Order 2. Crocodilia ( 

Order 3. Sauria (Squamata), ( 

Division I. Lacertilia ( 

Division II. Ophidia ( 


General Biology 

Class V. Aves ( 



Archaeornithes ( 



Neornithes ( 



Hesperornithiformes ( 



Ichthyornithiformes ( 



Struthioniformes ( 



Rheiformes ( 



Casuariiformes ( 



Crypturiformes ( 



Dinornithiformes ( 



Aepyornithiformes ( 



Apterygiformes ( 



Sphenisciformes ( 



Colymbiformes ( 



Procellariiformes ( 



Ciconiiformes ( 



Anseriformes ( 



Falconiformes ( 



Galliformes ( 



Gruiformes ( 



Charadriiformes ( 



Cuculiformes ( 

Order 20. 

Coraciiformes ( 

Order 21. 

Passeriformes ( 

Class VI. 

Mammalia ( 



Prototheria ( 



Monotremata ( 

Subclass II. 

Eutheria ( 



Didelphia ( 



Marsupialia ( 



Monodejphia ( 

Section A. 

Unguiculata ( 



Insectivora ( 



Dermoptera ( 



Chiroptera ( 



Carnivora ( 



Rodentia ( 



Edentata ( 



Pholidota ( 



Tubulidentata ( 

Classification 429 

Section B. Primates ( ) 

Order 9. Primates ( ) 

Section C. Ungulata ( ) 

Order 10. Artiodactyla ( ) 

Order 11. Perissodactyla ( ) 

Order 12. Proboscidea ( ) 

Order 13. Sirenia ( ) 

Order 14. Hyracoidea ( ) 

Section D. Cetacea ( ) 

Order 15. Odontoceti ( ) 

Order 16. Mystacoceti ( ) 



The principal groups of animals are given below with brief diagnoses 
which may serve as definitions. It must be understood that the charac- 
ters given will often not be sufficient to distinguish all the forms in a 
group, for there is much variation within the groups. They are intended 
to give the student a general conception of the phyla, subphyla and 

Phylum PROTOZOA ( ). Single celled 

animals without true organs or true tissues. If colonial, the cells are all 
potentially alike. 

Class RHIZOPODA ( ,. Protozoa with 

changeable protoplasmic processes (pseudopodia). Amoeba. 

Class MASTIGOPHORA ( ). Protozoa with 

one or more vibratile processes (flagella) which serve for locomotion and 
for taking food. Euglena. 

Class SPOROZOA ( ). Parasitic protozoa, 

usually without motile organs or mouth, reproducing by spores. Mala- 
rial parasite. 

Class INFUSORIA ( ). Protozoa having 

numerous slender vibratile processes (cilia), a cuticle, and fixed openings 
for the ingestion of food and the extrusion of indigestible matter. 

Phylum PORIFERA ( ). Diploblastic, radially 

symmetrical animals with body wall penetrated by numerous pores. 
Body usually supported by a skeleton of spicules or spongin. Sponges. 

Class CALCAREA ( ). Sponges with spicules 

composed of calcium carbonate, monaxon, or tetraxon in form. 

430 General Biology 

Class HEXACTINELLIDA ( ). Sponges with 

spicules composed of silicon, triaxon in form. 

Class DEMOSPONGIAE ( ). Sponges with 

spicules composed of silicon, not triaxon in form, or skeleton composed 
of spongin, or with skeleton of both spicules and spongin. 

Phylum COELENTERATA ( ). Diploblastic, 

radially symmetrical animals with tentacles, stinging cells, single gastro- 
vascular cavity, no anus. Two body forms are prevalent, the hydroid 
and the medusa. Jellyfishes, polyps and corals. 

Class HYDROZOA ( .^ ). Coelenterates without 

stomodaeum and mesenteries; sexual cells discharged to the exterior; 
hydroid and medusa forms in the life history of same species, or only the 
medusa, the latter having a velum. Polyps (including Hydra), a few 
corals, small jellyfishes. 

Class SCYPHOZOA ( ). Coelenterates with 

only the medusoid, not hydroid form; velum lacking; notches at margin 
of umbrella. * Larger jellyfishes. 

Class ANTHOZOA ( ). Coelenterates without 

medusoid forms, with well developed stomodaeum and mesenteries. Sea 
anemones, most corals. 

Phylum CTENOPHORA ( ). Triploblastic 

animals ; symmetry partly radial, partly bilateral ; eight rows of vibratile 
plates radially arranged. Sea walnuts or comb jellies. 

Phylum PLATYHELMINTHES ( ). Triplo- 

blastic, bilaterally symmetrical animals with body flattened, with a single 
gastrovascular cavity (sometimes wanting) and no anus. Flatworms. 

Class TURBELLARIA ( ). Free-living flat- 

worms with ciliated epidermis. Planaria. 

Class TREMATODA ( ). Parasitic flatworms 

without cilia but with a hardened ectoderm, usually parasitic and with 
attaching suckers. Flukes. 

Class CESTODA ( ). Parasitic flatworms with 

the body differentiated into a head (scolex) and a chain of similar joints 
(proglottides), the whole being usually regarded as a colony. Tape- 

Phylum NEMATHELMINTHES ( ). Bilat- 

erally symmetrical, triploblastic animals with an elongated cylindrical 
body covered with a cuticle, with a true body cavity, and a digestive 
tract with both mouth and anus. Roundworms. 

Phylum ECHINODERMATA ( ). Radially 

symmetrical (with minor exceptions), triploblastic animals with well 
developed coelom, and usually with five antimeres, spiny skeleton of 
calcareous plates, and organs of locomotion known as "tube feet" 

Classification , 431 

operated by a water-vascular system. Starfishes, sea urchins, sea 

Class ASTEROIDEA ( ). Free-living, typically 

pentamerous echinoderms with wide arms not sharply marked off from 
disc and with ambulacral grooves. Starfishes. 

Class OPHIUROIDEA ( ). Free-living, 

typically pentamerous echinoderms with slender arms sharply marked 
off from disc and no ambulacral grooves. Brittle stars. 

Class ECHINOIDEA ( ). Free-living, 

pentamerous echinoderms without arms ; the outer covering composed 
of calcareous plates bearing movable spines. Sea urchins, sand dollars. 

Class HOLOTHURIOIDEA ( ). Free-living, 

elongated, soft-bodied echinoderms with muscular body wall and tenta- 
cles around mouth. Sea cucumbers. 

Class CRINOIDEA ( ). Sessile echinoderms 

with five arms generally branched with pinnules, aboral pole usually 
with cirri, sometimes with jointed stalk for attachment to substratum. 
Feather stars, sea lilies. 

Phylum ANNELIDA ( ). Triploblastic, bilat- 

erally symmetrical elongated animals with external and internal seg- 
mentation; coelom usually present; setae common. True worms. 

Class ARCHIANNELIDA ( ). Marine 

annelida with no setae nor parapodia. Polygordius and Protodrilus. 

Class CHAETOPODA ( ). Annelida with 

setae and a perivisceral coelom ; marine, fresh-water, or terrestrial in 
habitat. Earthworms. 

Class HIRUDINEA ( ). Annelida without 

setae, and with anterior and posterior suckers. Leeches. 

Class ONYCOPHORA ( ). Annelida breath- 

ing by means of tracheal tufts, numbering from 10 to 40 per segment in 
irregular arrangement, with non-jointed papillate legs, nerve cords 
ventro-lateral, and without segmental ganglia, eyes of vesicular, annelid 
type, skin with chitin. This group is often placed with the arthropoda, 
or as a separate phylum proarthropoda, since its members have devel- 
oped somewhat in the arthropodan direction. Lankester thinks their 
evolution is as follows : 

Group Articulata 

1. Rotifera to Tardigrada 

2. Chaetopoda 

a. Proarthropoda (Peripatus) developing independently. 

b. Crustacea — separate origin from Chaetopoda. 

432 General Biology 

From Crustacea by separate origin 

a. Myriapoda 

b. Insecta 

c. Arachnida. 

Paleontologists, such as Walcott, the specialist on trilobites and 
worms, derive all arthropoda classes by separate lines from trilobites. 

Phylum MOLLUSCA ( ). Triploblastic, bilat- 

erally symmetrical (symmetry often obscured) unsegmented animals 
with a coelom, a muscular foot and usually a shell. Mollusks. 

Class AMPHINEURA ( ). Mollusks with 

obvious bilateral symmetry, sometimes an eight-parted calcareous shell 
and several pairs of gills. Chitones and Chaetoderma. 

Class GASTROPODA ( )'. Mollusks with a 

head and with bilateral symmetry usually obscured by a spiral shell of 
one piece. Snails. 

Class SCAPHOPODA ( ). Mollusks with 

conical tubular shell and mantle. Dentalium. 

Class PELECYPODA ( ). Mollusks without 

a head, with bilateral symmetry, a shell of two lateral valves and a 
mantle of two lobes. Clams, mussels. 

Class CEPHOLOPODA ( ). Mollusks with 

distinct bilateral symmetry and a foot bearing eyes and divided into 
arms, usually with suckers. Cuttlefishes, octopods. 

Phylum ARTHROPODA ( ). Triploblastic, 

bilaterally symmetrical, segmented animals with usually more or less 
dissimilar somites, a coelom very much reduced, paired jointed ap- 
pendages, and chitinous exoskeleton. 

Class CRUSTACEA ( ). Arthropods breathing 

by means of gills, two pairs of antennae, crayfishes, crabs, shrimps. 
Certain terrestrial species with tracheae (Oniscidae — sowbugs). 

Class MEROSTOMATA ( ). Fossil 

arthropoda of gigantic size (2 meters in length), without antennae, short 
cephalothorax, 12 segments in abdomen, and pointed telson. Eurypterus. 

Class POECILOPODA ( ). Arthropoda with 

large shield-shaped cephalothorax, abdomen with six pair lamellate legs, 
with extremely long pointed telson. Limulus, king crabs. 

Class LINGUATULIDA ( ). Parasitic 

arthropoda (Pentastomidae) of worm-like build, body with metameric 
circular muscles, two pairs of hooks in region of mouth, mouth without 
mandibles. Affinities uncertain. 

Classification 433 

Class PANTOPODA ( ). Marine arthropoda, 

body segmented, abdomen vestigial, with not more than seven pairs of 
legs, mouth a beak. Ammothea Pycnogonoides. 

Class ARACHNOIDEA ( ). Arthropods with 

either tracheae, book lungs or book gills, or both, and no antennae. 
Harvest-men, spiders, mites, ticks, scorpions. 

Class MYRIAPODA ( ). Arthropods with 

distinct head, one pair antennae, breathing through tracheae, whose 
stigmata are placed in linear metameric arrangement, many legs. 
Myriapods and millipeds, centipeds. 

Class MIRIENTOMATA ( ). Minute 

microscopic arthropoda (600-1600 micra), with six legs, a three-seg- 
mented thorax (?), no antennae, post-embryonic increase of segments, 
first pair of legs transformed into sense organ. These minute forms 
were only recently discovered, and their affinity is uncertain. 

Class COLLEMBOLA ( ). Arthropods 

with six-segmented abdomen, no post-embryonic increase in segments, 
one-jointed tarsi, few tracheae, these opening in one pair of stigmata at 
the throat, abdomen generally with spring. Snow-fleas, springtails. 

Class CAMPODEOIDEA ( ). Arthropods with 

long body, abdomen ten segments, with cerci. No eyes, mouth-parts 
withdrawn, no post-embryonic change in abdominal segments. Sprin- 

Class THYSANURA ( ). Arthropods with 

free mouth-parts and palpi, three caudal appendages, abdomen eleven 
segments and covered with silvery scales, frequently with spring beneath. 
Silver fish, fish moths. 

Class PTERYGOGENEA ( ). Insecta, 

hexopoda. Winged arthropods, with three pairs of legs, embryos with 
twelve segments to abdomen, adults with all degrees of post-embryonic 
reduction from twelve to six segments. Breathe through tracheae ; 
stigmata linear and metameric in arrangements. True insects — i. e., 
winged arthropods. 

Phylum CHORD ATA ( ). Animals having at 

some time during their life's history a notochord lying between the 
nervous system and the alimentary tract, a hollow central nervous system 
lying entirely on one side of the digestive canal, and pharyngeal slits 
extending from the pharynx to the exterior. 

( ). Fish-like chordates with a permanent notochord 

composed of vacuolated cells, such as amphioxus. 

434 General Biology 


Sac-like marine animals with a cuticular covering known as a tunic or 
test. This group possesses a notochord only in the caudal region. 
Example, tunicates. 

Subphylum HEMICHORDATA ( ). Worm- 

like chordates of doubtful systematic position. There is a projection 
from the mid-dorsal region of the alimentary canal similar to a noto- 
chord. These animals possess a collar and a proboscis. Example, 

Subphylum CRANIATA or VERTEBRATA ( ). 

Chordates in which the notochord either persists or becomes invested 
with cartilage. Vertebrates have a segmented spinal column. 

Class CYCLOSTOMATA ( ). Eel-like 

vertebrates without functional jaws or lateral appendages. Examples, 
hagnshes and lampreys. 


Fishes with a lower jaw and paired pectoral and pelvic fins, scales and 
paired nostrils. The heart has an auricle, a ventricle, a conus arteriosus, 
and a sinus venosus. 

Class AMPHIBIA ( ). Cold-blood vertebrates 

breathing by means of gills at some stage of their life-cycle. Skin not 
usually covered with scales. Three chambers in heart beside the conus 
arteriosus and sinus venosus. Frogs, toads, newts, and salamanders. 

Class REPTILIA ( ). Cold-blooded 

vertebrates breathing by means of lungs throughout their life-cycle. 
Usually covered with scales. Lizards, snakes, crocodilians, and turtles. 

Class AVES ( ). Warm-blooded vertebrates, 

whose body is usually covered with feathers and the fore-limbs modified 
for wings. Heart of four chambers. Birds. 

Class MAMMALIA ( ). Warm-blooded 

animals with hair covering at some stage in their life-cycle. They suckle 
their young and have a diaphragm between thorax and abdomen. 

Subclass PROTOTHERIA ( ). Egg-laying 

mammals. Example, monotremes, such as the Australian duck-bill. 

Subclass EUTHERIA ( ). Mammals which 

give birth to living young. These are the true mammals. 


These are the marsupials, such as the opossum and kangaroo. 

Division MONODELPHIA ( ). These are the 

placental animals which are nourished in the body of the mother through 
a true placenta. 

Classification 435 


Certain groups of invertebrates have not been assigned a definite 
relation to other groups. Opinion differs so widely as to their affinities 
that they may well be kept out of our regular classification for the 

Mesozoa. Parasites apparently intermediate between the Protozoa 
and Metazoa. Not improbably degenerate relatives of the flatworms. 

Nemertinea. Terrestrial, fresh water, and marine animals resem- 
bling flatworms but with a proboscis, blood vas